Saw something that made me pause

I went into the local coin shop last weekend to get some silver pieces (got a 08 ASE and a seventy something Mexican 720 silver piece, both raw, not intending on sending for grading) and I saw something that kinda bothered me. One of the workers was cleaning some coins using nail polish remover. Now, I know that using the main chemical in nail polish remover helps get rid of the marks from the PVC flips, but the owner of the shop told him not to do it while customers were in the shop.

Is this a sign that I shouldn't buy raw coins from them, and should just stick to Mint packages items if I am considering buying for grading?