What to do when your client can't sing!

I'm in a tough spot here. The vocal performance that a recent client gave was less than stellar. And with no hope of a better one. My question to you out there is what should I do? I want to record actual performances and make great records. Not autotune the crap out of everything. On the other hand they are a paying customer, and they don't think they are bad. But I can't, in good conscience let it go out as it is. My studio is new and reputation is everything.

If anyone out there has any advise, I would love to hear it.

Thank you as always for reading. \m/

kyle