Welder too cheap to be true?

Typically speaking you don't want flux core for sheet metal. You don't want to try welding anything thin with self shielding wire, spatter, burn through, more grinding needed on your welds, just overall not a good idea. Flux burns hotter and for thicker stuff it becomes more of an option. Gas is the way to go, not even a discussion needed on the subject when it comes to sheet metal, can you do it with a flux machine? Sure. Lot more effort, time and cursing... Plus the more you have to weld the same area the higher your chances of warpage.

Miller
Lincoln
Hobart
Esab
Thermal arc
Just a few brands to search. I would buy any of them used if I could test it first, before buying an off brand.

If your set on cheaper or that's all you can afford, buy from Eastwood, HF as they offer great warranties, I don't know if TS does? My plasma cutter is a HF unit and works great, 2 year warranty I figured I would try it. My welder is a Miller 211 and after trying Lincoln, Hobart and HF just no comparing them, Miller hands down in my opinion.

Welders have different options, tapped vs continuous, continuous is generally a bit more money and easier to dial in more precise compared to tapped. Tapped is selectable voltage generally by numbers, continuous is like a dial with no taps that you can turn down a hair, up if you need but generally both with do fine. My Miller is continuous with auto set, another nice feature but not really needed.

Of course 115 and 230 or both, the 230 generally let's you weld thicker metals, the 115 you can plug up almost anywhere and start welding. If you don't have a dedicated 230 in your garage that might also be an added expense. They also make models that are dual voltage, best of both world's. You can run flux wire and be really portable for that fence or that whatever needs welding where a dedicated 230 isn't as portable due to power requirements. That's where a dual voltage shines.

Didn't mean to ramble on but not sure of your knowledge level and wanted to touch on a few bases before you buy. Hopefully something in my ramblings was of use.