> A few years ago (>|decade?) music sales and video games were final at my local BB because they assumed you just burned yourself a copy.

Most places I've shopped just say something to the effect of no returns on opened merchandise. No mention of why. I assume you're assuming what they're assuming.

I don't like returning, generally, unless the product really didn't meat expectations. However, I've never had a problem returning opened hard merchandise.

> Would a big retailer (Best buy, say) accept the return of software whose seal has been broken.

Probably not. However, if you read a EULA, you will notice most of them have a clause to the effect of "if you disagree with this EULA, you can return the software" and AFAIK its usually with the company with whom the EULA is and not with the retailer (eg if you buy Microsoft software, the EULA (and therefore the return if you disagree with the EULA) is with Microsoft and not Best Buy).