It seems Danish Law Enforcement have developed a tool to track certain blockchain transactions:
The new specialized IT-system, developed by Danish law enforcement agencies, is based on comparing the information of two different types of bitcoin transactions. First, transactions where bitcoins are used to purchase goods are analyzed by exploiting the possibilities of blockchain technology, which bitcoin is based on. This information is then compared with listings of bitcoin-buyers and bitcoin-sellers.
From here: https://thenextweb.com/eu/2017/02/21/danish-police-hunt-down-criminals-using-bitcoin/#.tnw_IdxHqa3B
Maybe I'm offbase and just being hopeful but it seems this could be defeated by just obtaining and spending bitcoin in different amounts than are actually listed on the market sites. It sounds like what they're doing is using software to identify and make note of prices in btc on the marketplaces, and then going through the blockchain and looking for transfers for exactly or near that amount. If that's the case, buying btc in increments and using different wallet addresses, and transferring a bit more than you need or transferring to market wallets in increments, could fuck up at least one side of the profiling. Nothing to do about the profiling of market prices but obfuscating the wallet IDs that are sending to the markets via tumbling or using separate wallets to make the deposits seems like it would be enough.