When dealing with companies I have no prior experience of, I always use a Credit Card, simply because of the Consumer Credit Act which protects me. Then if they play pot, let the credit card company chase them.
On the odd occasion when a company refuses to accept a credit card, insisting on a debit card, alarm bells start to ring. My primary mission in life is to protect me, not them.
If they play pot, just walk away. There are plenty of genuine dealers who do play ball.