#1
I got my stratocaster set up about 1-2 weeks ago and ever since i got it back ive had a miserable time trying to keep it in tune. I had switched from 9s to 10s and had it set so the bridge was flush to the body which would "help keep it in tune better." the g string has been going sharp ever since i got it back almost immediately after tuning again to the point where its barely playable. i thought it might just be an issue with the string but the last couple days all 3 of the high strings have been going sharp on their own.

im thinking maybe they tightened the strings too tight? i would like to try to get this squared away without taking it back so if anyone has any suggestions they would be greatly appreciated
#2
I've had similar problems with guitars that I've owned, particularly with the three highest strings. I found that the strings were binding in the nut. I used a little graphite under the strings in the nut and it fixed the problem. It comes back every once in a while, but I put some more graphite in there and it goes away. Hope it helps.