I have had tips from my customers that i wont see until the new year, i have also refused (politely) tips from my elderly ones.
I cannot accept tips from pople that i know cant afford it, the response is always one of surprise but more importantly also of admiration, and i find you get referrals from these older customers, so in a way my morals make me more money than a one off couple of quid and i sleep soundly!