ORIGINAL: bruce88123
$20/gal is too high for 15% fuel anyway but 15% is fine for your engine, $15 would be a more typical LHS price(depending upon brand). I'm kinda surprised they offered to tune it in the first place. My LHS's wouldn't even know how, they are train people.
Where the heck are you shopping?? My LHS has it at $22. They aren't plane people either and wouldn't know the first thing about tuning.
Back to the original post: I agree with the other comments. Just based on your writing and comments it seems you're a bit aggressive in the first place. Try working with them instead of against them. Ask questions and try to learn how to do this yourself rather than just have others do it for you. Express interest and a willingness to make an effort and I'd bet you'll be a much happier person... and not just in this hobby.
Good luck to you!