Something done in commercial work that I've never seen done privately is to withhold 10 to 20% of the total cost (as per estimate) until the problems on the "punch list" have been corrected.

And be CERTAIN of what is to be done -- specify, specify, specify! Be sure that you specify "3/4 inch exterior grade plywood with both sides good" if that is what is needed and wanted.

I'd even suggest writing up a Request For Proposal (RFP). At the very least put down in writing what you'd like to see done -- this sort of project is too, too, expensive to be indecisve or vague about.