Hello,
Personally, I like to speak with the seller on the phone.
Of course, you should get them to email a synopsis of the agreement to you....so that you have documentation.
But, by talking with someone on the phone you can often pick up on certain things that you might possibly miss in an email.
Talking one on one... person to person can help to give you a feel for whom with you are considering dealing.
The sellers reputation is important.
I have dealt with some new people who were really great.
But, it can pay you to check their reputation out BEFORE dealing with them. Ask for references.
Check the BOI.(sometimes this may or may not be helpful.)
Ask who they purchased their breeder stock from.
Then, call THAT breeder and see if they had a good experience selling to this person.
Knowing a little of the history of your potential seller's dealings can be very helpful when you are trying to make a decision about working with them.
Above all, make sure you feel comfortable about the deal.
If you have that little voice of skepticism nagging at you and you feel a bit uncomfortable.....DON'T IGNORE YOUR INTUITION.
Usually people are pretty good at picking up on ques that should make us uncomfortable....the problem is that many times we fail to listen to that little nagging voice of skepticism.
It is easy to get caught up in a "great deal"...only to later regret listening to our own intuition.
Avoid anyone who seems pushy.
Most of the people in this hobby/business are genuinely of good nature. Keep that in mind...but keep your antennae up! 
Go over all the sticky questions about the sellers guarantee policies and the "what happens if".... before you send a dime.
Get it in writing (email is fine)...then proceed, if you feel right.
Most good sellers understand that the most valuable item they can ever offer is a positive reputation.
It can take years to build such a reputation...and only moments to destroy it. Working with a seller who has built a solid and well deserved reputation can be very rewarding.
Use a credit card via paypal...this can serve as a double firewall for you. You are afforded some protection from your card's policies...as well as paypal's protection policies.
Best of luck to you.
Take care.
Your friend,
Harlin Wall - WALL TO WALL REPTILES!
970-245-7611
970-255-9255