My ear tells me this is correct:
"The best I can do is give you a refund."
But what is the verb in the above sentence: "is", or "give"? I think "The best thing we can do" is a subject phrase, and I think "is" is the verb, but I'm not sure what's going on with the infinitive "laugh". I'm pretty sure "is give" isn't a valid tense.
Would it perhaps be safer to say, "The best thing I could do would be to give you a refund?"
Thanks for any insight -