I've had 2 tubs refinished. 1st didn't last more than a yr. and the guy was no longer in business. 2nd time I just made sure to find a reputable person that was in business for 10 yrs and had lots of referrals. Both warranties were the same ... 1 yr. but as I said the first guy was no where to be found. The 2nd guy said that his job will last at least 5 yrs if not longer when properly cared for.
Like the other poster mentioned, some just don't do it with the same skillfull process.
I learned after the first time that once the finish is cracked in any way, it can quickly deteriorate. My son used to take his toy trucks in w/ him and little scratches would happen. I also put a ladder in the tub with not enough padding to paint the ceiling and that didn't help either.
With the 2nd finish, I was a lot more careful with the tub and it's been 3 yrs and still looks great. Use what they recommend for cleaning.
Oh, and one other thing - the first time the guy put a permanent slip resistant mat in the tub. (very very slippery w/o something) They dont recommend suction type pads. The 2nd guy put something bumpy - not sure exactly what - under the glaze. (It could have just been a material process and not a mat per se) Worked much better for slip resistance and not so scratchy.
Hope this isn't too long, but I like to hear others actual experiences with these kind of things. Hope it helps you with your decision.
Beth