There are way too many opportunists in Venice trying to somehow get money out of you. The one I stumbled upon the most was guys offering me flowers, usually a rose. Some would try to sell it at exorbitant prices at once, some would say it was a gift, since I was such a lovely girl.. and the nag me into making a ‘donation’.
If you say no from the start and just keep walking they will keep trying as long as you’re within earshot… but if you take the rose by accident, reflex or innocence… they might chase you for blocks.
Always give a hard no for an answer… but if that’s not enough, tell them some pickpocket took your wallet and all your money. They get away from you, just in case.