I know you're looking to stock a store, so I'll just tell you what I would do. This is just my opinion.
For the sake of stocking a store, you should have a broad range of products, since many customers already have their minds made up on what to use before they come to the store. If you don't carry it, you lose. If you can find aspen shavings for a good price, stock it in BALES, and recommend it to anyone who asks. It seems to be universally acceptable for most non-humidity loving snakes and even some lizards. Repti-bark is good to have on hand. Carefresh is another hugely popular substrate, as is Beta Chip. Get lots and lots of sphagnum moss too. Calci-sand is garbage. That's my $0.02, should give you plenty of options.