There are some things you can’t buy until you are 16 or 18. But when you do legally buy things, whether they are “goods” (actual things such as clothes or electrical equipment) or “services” (such as a haircut), you will have the same rights as an adult (under the Consumer Rights Act 2015, if you’re interested).
If something you buy is broken or damaged, doesn’t do what it’s supposed to do, or isn’t as described by the seller, you may be able to get a refund, replacement or repair. This applies however you bought it (new or secondhand, from a shop, online) but does not apply if you have just changed your mind – shops and companies often do accept returns for this reason, but are not legally required to.
If you think that the person supplying the service did not act with reasonable care and skill, you can ask them to do it again (if that is possible) or ask for a discount. More detail can be found here.
You might also be interested in our other pages on your legal rights: