I always measure mine...One very popular retailer just shorted me last week. They mailed me 45" wide when I had ordered and paid for 108" wide marbled fabric. (Really, I didn't have to "measure" that one...it was obvious.) I made 3 calls to them over 5 days and kept getting the excuse that the man I had to talk to was "out of town", or at lunch. Finally got to talk to that man yesterday, and I hope they make good on their promise to fix the error, because I am really waiting for this fabric.
On the other hand, I have ordered from Joanns a couple of times over the summer, and both times they have ended up sending me at least 8 - 10 inches more than I ordered on a couple of pieces of yardage. I guess they just got tired of measuring and cut it where they felt like it. :O)