While trying to find a trustworthy store, I noticed that many of them boast about having a 70,000 sqft warehouse, and all use the same checkout system. I eventually figured out that most of these sites are just dropshipping via instantonlinepoolstore.com (also known as Under The Sun Distribution). Some of the stores using this system:
Reviews seem to be mixed, with customer service and up selling being a big issue. Is there really no 'top dog' in this field (like Newegg, but for pools)? I guess I'll have to check local stores again, but all I want is to buy a 24' AGP liner from a company with an awesome customer service track record.