How do you determine which utxo is tainted, take note that there is nothing such as tainted BTC,
Ask any chain analysis, it's just the same idea of dirty money/cash as we're talking about money where is nothing such "dirty cash" as all.
Anyone can use a gambling site or a privacy solution, and it does not mean they are involved in anything illicit.
Of course, but whatever you say the point is funds from these platforms are considered as high risks and higher chance of getting confiscated in any CEX, not just for any reason but for this exact reason especially funds from privacy solutions. While unreputed and new exchanges probably will confiscate your funds almost for any reason, scam accusations board is the witnessed.