What specific techniques or cryptographic tools can a user utilize to make a cryptocurrency transaction completely untraceable, explain the limitations and possible risks of using those tools.

Achieving complete untraceability in cryptocurrency transactions is an extremely challenging, if not impossible, goal. While various techniques and cryptographic tools can significantly enhance privacy and reduce traceability, they often come with limitations and risks. It’s important to understand that no single technique can provide absolute anonymity, and a combination of methods is often needed to improve transaction privacy.

Here's an overview of specific techniques and cryptographic tools, their limitations, and associated risks:

1. Privacy Coins:
- Techniques: Privacy coins like Monero (XMR), Zcash (ZEC), and others employ advanced cryptographic techniques to obscure transaction details. Monero uses ring signatures, stealth addresses, and confidential transactions to hide sender, receiver, and amount data. Zcash uses zero-knowledge proofs called zk-SNARKs to shield transaction details.
- Limitations: While privacy coins significantly improve transaction privacy, they are not completely untraceable. Metadata about transactions, such as the timing of transactions and associated IP addresses, can still be potentially linked. Additionally, the level of anonymity provided by these coins can vary depending on how they are used. If a user makes many public transactions linked to an address, and then later makes a private transaction, the linkage may still be possible. Also, privacy coins are less widely adopted than Bitcoin or Ethereum, and their utility is not as robust as more widely supported chains.
- Risks: Privacy coins are often viewed suspiciously by regulators and law enforcement, due to their ability to obscure transactions, and their use may attract additional scrutiny. There is always the risk of being associated with illicit activity by holding privacy coins.

2. Coin Mixers/Tumblers:
- Techniques: Mixers combine a user's cryptocurrency with those of many other users, then send the funds back to new addresses controlled by the original user. The purpose of this is to break the on-chain links between the input and output addresses of a transaction.
- Limitations: While mixers can make transactions harder to trace, they are not fool-proof. Some mixers can be tracked by sophisticated blockchain analysis techniques. Also, using a mixer often raises red flags to law enforcement agencies. Additionally, mixers often rely on trust in the operators, and can potentially steal user funds or log transactions.
- Risks: The use of mixers can raise suspicion from law enforcement agencies, because it can be seen as evidence of an attempt to hide financial transactions. Also, some mixers are malicious and designed to steal funds, and most mixers are not regulated, which can lead to issues.

3. Decentralized Exchanges (DEXs):
- Techniques: Decentralized exchanges allow users to trade cryptocurrencies directly with each other, without an intermediary. DEX transactions are peer-to-peer and not controlled by a central entity, which can add a layer of privacy.
- Limitations: While DEX transactions are not directly linked to centralized exchanges, the blockchain still records the transactions, and these can be linked with the user's wallet addresses. Also, if the DEX has an order book, the transactions are usually publicly available and can be analyzed by blockchain analysts. Also, some DEX’s require KYC (know your customer) verification.
- Risks: Some DEXs may have poor security implementations and are subject to hacking or other vulnerabilities. Also, some DEXs do not have enough liquidity.

4. Layer-2 Scaling Solutions:
- Techniques: Layer-2 solutions, like Bitcoin's Lightning Network, allow for off-chain transactions. Transactions occur between users on the layer-2 network and are only periodically settled on the main blockchain.
- Limitations: While Lightning Network transactions are not visible on the main blockchain, the opening and closing of channels between participants is visible. Also, there are limits to how much can be transferred via Lightning Network.
- Risks: Using layer-2 solutions often means trusting third-party nodes or hubs with your funds. There can also be risks of channel failures or other technical complications.

5. VPNs and Tor:
- Techniques: These tools obfuscate a user's IP address and location, making it harder to link transactions to real-world identities. VPNs route internet traffic through an intermediary server, and Tor routes it through a network of relays, and helps to make web traffic anonymous.
- Limitations: While VPNs and Tor help obfuscate IP addresses, the cryptocurrency transactions themselves are still public and can be tracked on the blockchain. While VPN’s and Tor can make it harder to identify a user by their online behavior, it does not make cryptocurrency transactions untraceable on the blockchain.
- Risks: Some VPNs may log user data, and the Tor network can be slow or unstable and may also log user data. Using Tor may also raise suspicion with internet service providers or other networks, as it is often associated with suspicious behavior.

6. Using Multiple Wallets and Addresses:
- Techniques: Instead of using the same wallet and address for all transactions, create a new address for every transaction. This minimizes the association of your identity with multiple transactions. Additionally, using many different wallets for different functions can help to separate your activity.
- Limitations: While this makes tracking harder, it does not make it impossible to trace, especially with sophisticated blockchain analysis. This method is not very effective if the same exchange or service is used to send funds to multiple wallets.
- Risks: Managing multiple wallets can be cumbersome and can lead to errors or accidental fund loss if not properly handled.

Examples:

A user who wants to keep their cryptocurrency purchases private might use Monero to make the transaction. This transaction, unlike a Bitcoin or Ethereum transaction, would not reveal the sender, receiver or transaction amount, making it much harder to track. However, if they are linked to that transaction in some other way, it is still possible to link the activity.

A user sends some Bitcoin to a mixer, and then after a series of mixing transactions, receives it in a different wallet. This makes it harder to track on the blockchain, although the mixer itself, or the mixer's transactions, may be identified by blockchain analysts.

A user making a purchase on an online marketplace may use the Lightning Network to send Bitcoin. This hides the transaction from the main Bitcoin blockchain, however, the on-chain settlement may still be identified.

In conclusion, while several techniques and cryptographic tools can significantly improve transaction privacy, there is no foolproof way to make a cryptocurrency transaction completely untraceable. These methods often come with limitations and risks. A combination of these methods, a thorough understanding of their nuances, and an ongoing awareness of the latest techniques and threats are needed to maintain a strong layer of privacy.