What should I be looking out for when buying a puppy?

I've found the perfect miniature dachshund pup on gumtree, and I just want to make sure I don't get scammed or played a fool in any way, since it's my first time ever buying a pet

What are some things I should be asking the breeder to provide/verify, and some things I should be looking out for like any red flags, etc

I just want the smoothest experience for acquiring the little guy and don't want to get scammed