I wouldn't ever endorse a piece of shit product, no matter what I was paid to do it for. Of course, I assume that if I were asked to endorse a product, I would already be in some sort of good standing and in the public eye, which would make it likely that I'm already earning pretty good money.
When thinking of this sort of thing, I am always reminded of an article by Hunter S. Thompson about Jean-Claude Killy and his post-Olympics endorsements for Chevrolet. Thompson worries about the possibility that athletes like Killy will more and more frequently demean their athletic accomplishments-accomplishments that regular people see as beyond extraordinary-by shilling for a few extra bucks.
About Killy, Thompson concludes while watching Killy's selling of himself that "nothing in his narrow, high-powered experience can allow him to understand how I can watch his act and say that it looks, to me, like a very hard dollarÃ¢??maybe the hardest."
I suppose for me, it's a matter of how much money it would take to outweigh my dignity. I think at some point there is a price, because at some point there is an amount of money that would seriously change my life for the better. It would still have to be pretty high and it would also depend on the product. There's no amount of money I would shill cigarettes for, for example. If I were someone of some significant renown who would be a likely endorser of something, the price would have to be very, very high, to the point where it isn't likely I'd be paid that amount.
Besides, I probably wouldn't do well with all that money anyways. The worst thing that could happen to someone like me would be to win the lottery; I'd just turn into a bum and probably be dead within a few years.