[henry quirk]

Hey, that's fine by me, so long as the option to not participate is part of the deal.

Why would someone opt of such an apparently good deal?

Perhaps the plumber in question is just lousy at what he does: I may not see the value in getting crappy work done for half-price.

Or: if I'm a plumber myself, it would be pointless for me to go in on a deal to pay for services I provide to myself.