How to buy used car in Houston. New to USA

Hi Everyone. I’m moving to Houston from Canada. I was wondering if anyone can give me any tips and tricks for buying a used car. Personally I’ve bought used cars in Canada off Facebook Marketplace but since I don’t know the whole process I was thinking about using Carmax or Carvana. Was wondering if people on here could give me some tips. I looked on Facebook Houston marketplace for used cars and seemed like a bunch of them were scams