Not tech-only, but helpful and not everyone knows these tips, which apply to shopping in person and for item 4 online or by mail order or telephone - from the good ol' UK BIS, so mostly relevant to UK consumers only, I've added the bits in italics:
1. Not my style – some might be surprised to learn that you do not have a right to a refund if you simply decide you don’t like what you have bought.
2. Six month rule - if you make a claim for a repair or replacement of faulty goods within six months of purchase it’s actually up to the retailer to prove that the goods were not faulty when sold to you. [Note: this may not help if you're buying from outside the EU, or indeed possibly even the UK.]
3. No receipt required - you do not need a receipt to obtain a refund for faulty goods. However, you may be required to show proof of purchase with a credit card slip, bank statement or cheque stub.
4. Online is fine - if you buy goods on the Internet you also have the right to a seven working-day ‘cooling off’ period from the date you receive the goods, with the right to a full refund regardless of the reason for return. [Note: this applies to phone orders or mail order too, but it only works when you're buying from a retailer in the UK or EU. You need to tell the seller within 7 days of receipt that you want to return the goods, but you don't actually have to return the goods within 7 days, as long as you do return them ASAP and certainly within 30 days, safest to take that as 30 days after the order or at most 30 days after receipt. Buying from outside the EU e.g. the US is another matter, and much, much riskier for EU consumers - I'm planning a different blog post on that as I've been burned myself.]
5. Returning it to the retailer - when you buy goods, your contract is with the retailer not the manufacturer and you should always go back to the retailer to make a claim.
6. Fit for purpose - the goods you buy from a retailer should be fit for purpose and of satisfactory quality. If they are not, you are legally entitled to make a claim for a refund, repair or replacement. [Again, you will likely encounter problems in practice if you're buying online from outside the EU, e.g. the USA, even if the goods are faulty.]
7. Act quickly - if goods are faulty and you wish to claim a full refund you must return the goods to the retailer within a reasonable period of time.
8. Smarter sales shopping - you are not entitled to a refund on sale goods if you were made aware by the retailer that the goods were faulty or if the fault was obvious. Also, if you change your mind about liking the goods you aren’t entitled to a refund.
9. Nearly new –you have similar rights to a refund, repair or replacement as you do for new goods but remember that the law doesn’t expect second goods to be of the same quality as new ones.
10. Stick up for your rights – if the retailer is failing to acknowledge or respond to your consumer rights, in the England and Wales, you can file a claim (under £5,000) with the small claims court.