Welcome!
It depends on what is important to you. If you want to be able to handle the snake & see it in person, before you take it home, a pet store is an option, but there's also reptils shows that breeders will go to & have snakes for sale. This is a great option, if you are able to get to a show. From what I;ve heard, prices are pretty good at shows.
I have ordered a few snakes online, & if you trust the person/breeder, this is a perfectly acceptable way to obtain snakes. You won't get to see the snake (other than pics) until the snake is delivered.
If the one in the pet store looks healthy, & no visable signs of mites, & if you really like it, there's no reason you shouldn't get it.
There are several great resources on here, to get snakes from, both babies & adults.
Beware, they're addicting.
