I see that you already bought the snake and congratulations!

Just in the off chance someone in the future stumbles on this thread I will share the one tip I can contribute that nobody here has mentioned.

Mites are one of the major issues you DON'T want to bring home with you when you buy a snake. I was advised by a local breeder on how to properly check for them before purchasing. If the snake is small, you want to be VERY CAREFUL when you're holding their head and neck.

You want to check the area under their chin. There's a little cleft there that expands when they're swallowing food to allow their mouth to wrap around it more. It looks like a little butt crack. If you carefully hold the snake and check that area using your fingers to spread and move the skin and reveal the scale-less area between the crack, you can often catch mites by finding them hiding in there.

His source for this tip: he worked at NERD for several years.