Quote from an old girlfriend: become familiar with the store's return policy before making a purchase.
Suppose someone buys a piece of software with the intention of using it on two computers (but with him being the sole individual using it, and with him only actually using one copy at a time). General copyright law has no problem with this, and many companies' license agreements allow for it as well.
If this person spends $400 on this piece of software, takes it home, goes to install it, and discovers that the license forbids such installation, what is he supposed to do?
If the software can be returned in such case with the purchaser receiving full reimbursement for any monetary costs incurred in its purchase and return, the license might be enforceable. But if it cannot, the license is void.
He is supposed to take it back to where he bought it and get a refund. This may be easier said than done. If the store balks, the store manager should read the applicable clause of the EULA: YOU AGREE TO BE BOUND BY THE TERMS OF THIS EULA BY INSTALLING, COPYING, OR OTHERWISE USING THE PRODUCT. IF YOU DO NOT AGREE, DO NOT INSTALL OR USE THE PRODUCT; YOU MAY RETURN IT TO YOUR PLACE OF PURCHASE FOR A FULL REFUND.
In order to be "allowed" to sell the product, the store must agree with the manufacturer to take returns. This is usually the way it works. If the store still doesn't want to play ball, then you take it up their management chain. When you reach the end of the chain, there's always the FTC.
Some fella in Oz actually got a refund for OEM-installed MS software from Toshiba, but it wasn't easy.