I doubt that the coins are tainted because I never got to the point where I had to fill in input address.
The problem is that they give some imaginary rate of 3046722 BTC for 27 USDT. When I try to proceed just get error:
I don't know what they are doing with this rates but you better ask them directly with support.
For their so called ''tainted'' claims they don't really have to ask you anything, they clearly stated they can just charge 3% higher fees, and I am not saying your coins were marked as that or not.
Anyway, I am sure OrangeFren stuff will also get in contact with them about rates.