It's illegal to do illegal stuff, but it's not illegal to do off-label usage stuff. If I want to take your hydrogen peroxide you sell as a surface disinfectant and mix it with vinegar and salt to etch my PCBs at home, that's my prerogative.

Well, who's gonna tell on you? :) I don't have a bottle of H2O2 handy so I don't know if it normally has that disclaimer.