I think anyone that owns a guitar accepts the fact that they’re going to get dents and scratches on it. No matter how cafeful you are, it will get nicks and bruises on it. A lot of times it is just the finish that gets damaged, which isn’t that big of a deal. But sometimes you get a dent and the vast majority of people really don’t know how to repair such damage.
There is no need to get wood fillers or some sort of device to help pop it out because you can take care of this with water. If you put a small drop of water on the dent you will see the that wood will absorb it. As it absorbs you will notice that it swells and eventually gets back to the original look. Remember this is for a dent, not if you chipped it or something along those lines. There is no fixed time on how long the water should remain on the dent. Sometimes a minute is good enough and longer.
When it comes to scratches people seem to like the idea of sanding down the wood around the scratch. It makes sense because it levels out the wood and you won’t see it, but you probably are just going to make a mess. All you have to do is apply shellac to the guitar. You might think that this is varnish, but it isn’t. When you look at the end result you might assume they’re the same too. Varnish is something that is absorbed right into the wood, where as shellac stays on top of the wood. It’s much better at getting rid of the scratch.
Typically you have to buy a large can of this stuff and you’re only going to need a little for scratches. So if you’re looking to save money than just use clear nail polish. It’ll fill in the scratch and it will disappear.
Shellac is a great thing to have though. If you buy older guitars that you want to fix up, than you’re going to have use Shellac on it. People will probably tell you varnish, but that’s not what you want.