Door trimming-How much should I offer

[Mary R.]

A Friend is taking my four hollow core panel doors to a friend of his to have him trim them to size with his table saw. How much is appropriate to offer him for this work. The fellow volunteered to do it free, and I appreciate that, but I don't know him and feel I should at least offer. i don't want to either insult or over pay.
What's it worth? Quick trim of 4 doors with a table saw by a man who knows what he's doing, vs hand planing and sanding by a man who doesn't really know?
Thanks.
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