As you noted regulations can very widely across jurisdictions therefore Caveat Emptor feels like the rule of thumb to go by.May I ask, lots of people here in this thread and elsewhere talk of store policies. Aren't there laws that regulate this sort of thing? I understand that they differ from country to country, or state to state; but surely in most places, there must be some sort of regulations that overrule any store policies? Like, for instance, 14 days to exchange or return an item if it hasn't been used and has all the packaging and tags attached?
E.G.

Return Policies and Refunds - FindLaw
while merchants are not required to accept returns (unless there is a defect, in which case it may be covered by an implied warranty), certain laws govern the disclosure of refund and return policies. The following information covers the basics of refunds and return policies in general.

Office of Consumer Affairs
Practical tools and information to help protect consumer interests. Published and designed by the Office of Consumer Affairs of Industry Canada.

Canada Goose Takes Heat for No Refund Policy in China
Canada Goose is under fire again after refusing to refund a Chinese customer. How will this affect the parka maker during its peak selling season?