Airsoft is a pretty rough sport, and although there is not a lot of direct contact between players, there is still a lot of running and jumping that occurs during games. Because of all the movement, incidents happen in which an airsoft gun may be damaged, or could break. Sometimes the damage is too severe for the product to be adequately repaired, and you need to get a new gun to replace it. This is not the case all the time, and if you can fix the gun, it is often cheaper to do so then buying a brand new piece.
There are many cases when you can do all the work required to repair airsoft guns. This is usually possible if the damage is fairly superficial, and all you need to do is replace a few external parts in order to get your device working again. If you have some experience working on the internals, then even if something inside breaks, you can just order the internal parts you need online, and then install them yourself. Not only does this save you money, but it makes you a more experienced airsoft player, and it always feels good to be able to explain to someone how you did something yourself.
That is not to say there is any shame in outsourcing the work if it is too difficult for you. If you want to fix your airsoft gun, but you feel you cannot do it yourself, you can take it somewhere to get fixed for you. In the case you take this route, you will need to pay for both the parts and labor of the repair, so it will clearly be more expensive than if you did it yourself. But if the only way is to pay someone a fee, then that is what must be done.
To decide whether it would be better to carry out a repair or replace the airsoft product entirely, just figure out which way is cheaper. This decision should not be motivated by much else than price, although if you do feel an attachment to your current gun, that may be a factor that would entice you to carry out repairs rather than do a replacement.