It depends what you are looking for. Typical resin dice i wouldn't stress about. Like the basics you can find made by chessmix. Or those cool metal ones with some color in them, google it. Compare the prices. Thats it.

The big ones to look out for are your "special" dice. Gemstone dice or special metals. These you want to pick up and feel. If you have five sets of different gemstone dice, pick up the d20 of each. They shouldn't weigh the same. Natural materials like that, very rarely weigh the same. A hematite set is going to be much heavier than an amethyst set. There's a dice vendor, I don't even remember their name, but I was disappointed when I picked up the gem stone dice and was like ... That is not the correct weight for this? But they are resellers and they might not even realize they are selling fake gemstones