A lot of people prefer replacing their car's brakes by themselves and have enough expertise to pull this off with minimal complications. Even for someone not so proficient in the area, it is possible to gain the correct know-how from a source that they trust, and achieve basically the same result. The approach sure saves a ton of money each time, but like with most things of this scale, it can easily go wrong if you do not know what you are doing.
Changing your brakes is not as simple as swapping the parts and then pouring some brake fluid. Good maintenance requires a more involved approach than that, and the project could turn too complicated if you start it without a solid plan.
One good example is that of unevenly worn pads, which may result from sticking or dirty caliper pins. Sometimes, the calipers need to be cleaned, replaced, or lubricated. You may see too much pedal travel resulting from air having entered the brake lines. You may discover the need for a master cylinder replacement, or a new brake piston or caliper. You might start off planning for a simple brake pad replacement, but the job could become a lot more complex when deeper problems reveal themselves.
A grinding sound that you chalked up to worn out brake pads could actually be the result of a faulty rotor. If the brake pedal feels weird after finishing the job, or you hear squealing noises, the whole process of checking for problems may need to be fully repeated. At times, all that you have to do is top the brake fluid or add some brake grease to limit friction. In other scenarios, the car's brake system may be required to undergo a more in-depth diagnosis.
If you lack the requisite knowledge, tools, or experience to tackle the issue, replacing parts by yourself is not a good idea. You may know your car a lot better than anyone else does, but nine times out of ten, a qualified mechanic could soundly beat the benefits of that through sheer expertise and experience. Repair shops are also a better bet when you want guarantees on new parts fitting and working well; it means that if anything failed to work right after a repair job, these people would be there for figuring it out and fixing the underlying problem for you.