Advice on avoiding dodgy cars on Autotrader

I only have a very small budget, maybe around £2,500 and looking to purchase a second hand car on Autotrader

I'm mainly looking for something that's basic, something like a Toyota or Citroen seems to be sensible and reliable

I know because I only have a small budget I might run into some dodgy sellers - I don't know much about what to check for and what sellers to avoid

Would I have slightly better protection if I purchase from a car dealer and pay via credit card if anything goes wrong I have some recourse?

Some friends have also advised that cars with a long MOT is not completely foolproof because there are dodgy MOTs out there

Not sure if it's a thing if I can insist that the car gets an MOT with my own mechanic and I cover the cost, or is it not a thing to ask for?

Would appreciate any tips or advice

Thank you so much