My general advice would be to try to find a company that lets you select the individual parts like G. Skill 16GB (2x8) 3600Mhz vs a generic +16GB RAM upgrade (just an example and not a hard rule). Stuff like Origin PC and iBuyPower or whatever is local to you.
That way you avoid stuff like Dell and other big OEMs. You’ll probably pay a bit more but that way you know exactly what you’re getting in terms of quality. It’s easier to look up reviews on individual parts than a whole prebuilt and they will likely be priced by quality.
That being said, if you know anyone who’s put together their own PC or is the “computer person” maybe ask them for help with choosing those components.
A PC needs 7 main components: CPU, motherboard, GPU, RAM, storage, a power supply and a case.
Your choice of CPU and GPU can come from any youtube channel like Hardware Unboxed. Your motherboard, RAM and storage doesn’t matter much tbh. Your case should have good airflow (anything with mesh really) and your power supply should be rated gold ideally from a reputable brand with enough headroom for your components (750W will cover most mid-high end stuff, 550W is likely fine for most). And you can figure out how much they’re charging you extra for the building and warranty by checking how much the components cost on their own.
If you can make those few decisions then you’re most of the way there barring the company techs messing up but if it performs as expected in games and temps are OK when you get it then you should be good to go.