Ashton Crusher wrote:

I think you are doing almost the right thing. You should give him
the whole rebate, don't hold out that $1. It's such a small amount
it's meaningless as far as money but think of the impression it leaves
to people (and your customer) who hear about that measly $1 - It makes
you sound like a real chiseler even though you are giving the other
$29 dollars away. If he tells the story to his friends what will they
remember, that you gave him the $29 or that you kept the lousy $1 ? If
you give back the whole $30 you come off like a 100% upstanding guy,
if you keep the $1 you just come off as cheap, no one will remember
the $29.

Old car salesman adage: "I'd rather sell one guy five cars than five
guys one car."

Building good will brings in long term business and creates positive
word of mouth. I have bought three used vehicles from the same
salesman and referred two more people to him who have bought their
vehicles from him too.