Need some advice

So I haven't done any art stuff in a while. Real life just busy and kicking my ass. LOL

Anyway I previous customer contacted me asking if I have any problem with ownership/copyright approval, that they were considering putting them on other products for gifts and personal use... and they also said "no major production/distribution involved, but you never know"

I've never sold/given up copyright ownership to any of my work before so not sure if I should do it, say no, or get a chunk of money and sign it over? What if that slight chance it gets put on stuff that ends up selling and they start making a profit. Obviously if I signed over rights, they'd get everything and me nothing. I doubt my stuff would sell but in that slight chance it did and got distributed.... well, I'd atleast like to be compensated for all that time and work I did creating the character and stuff.

What would you do?