It depends, if they are tainted linked to millions of dollars from selling drugs they may bother. You never know who sent you the coins. The problem is evident. They would try to contact theymos I guess, then check logs and so on. But im talking about buying in real life. You buy something in real life, and they will know who you are, even if you don't exchange personal details, you showed your face, there's cameras everywhere nowadays etc. If you don't see a problem of using BTC to pay someone and end up in some sort of investigation about drugs or whatever then I don't know what to tell you.
If you pay face to face, what is the difference between choosing Monero, Bitcoin or FIAT? Cameras will still get a picture of you. The vendor will also know your face.
If you pay online, you must use a shipping address. This detail will be the same, no matter if you use Monero, Bitcoin or FIAT.
It is basically a lottery everytime you deposit or pay someone with BTC where you hope your coins are not tainted. Chances are very low yes, but it's still there.
How is this different for what I said above? I will quote myself again:
If you are worried that you own coins from illegal activities, let me tell you that anyone potentially owns this kind of coins, even if we use coinjoins.
If you don't see a problem of using BTC to pay someone and end up in some sort of investigation about drugs or whatever then I don't know what to tell you.
I never said that it is not a problem. All I said is that I find it pointless to try to avoid it. If someone gives you $100 in dollar bills and you try to deposit at a bank, then if the serial number of the bills is flagged by the authorities, you will have the exact same issue. I am just saying this because it looks like everyone who uses the "tainted" coins arguments seem to forget it.
Anyway, it is obvious that we have very different opinions and that you follow the "tainted" coins approach / idea. I don't think we will ever agree, so, I think our arguments have been said and anyone can make their own opinion reading them.