Wow, iDiveChick, remind me not to sue you ...
This brings up an interesting point. In Canada, there is only a law that the tank must be hydro'd every five years. But there is no law at all saying a tank must be visually inspected annually. I believe it is the same in the US. That is a dive industry standard, but not a gov't regulation. Even though outfits like PSI started a program to train visual inspectors, there are no gov't standards or applicable laws, and in actuality it is true that any Joe can stick a vip sticker on his tank and be just as legal as the guy who took a course from PSI, TDI or whoever.
That being said, obviously a dive shop is allowed to refuse any tank any time they want on whatever grounds they want. It may not be good for business but it certainly is within their right. And I would think there would be an argument for lack of due diligence if annual vips are at least a dive industry recommendation and yet a shop ignored it and there was an accident.
Another note: several folks around here went out and took visual inspection courses from different agencies so they could inspect their own tanks, but then some of the same shops that taught them won't accept their tanks because they weren't inspected by a "shop". This is more a case of being petty about losing a couple bucks on the inspection, but ...