Just a few suggestions:
Do a little research before sending any money. Google the vendor's name and/or telephone number. Contact their local BBB. Ask on a forum if they are reliable.
When the transaction is completed, post a review. If they screwed up, warn us. If they did a good job, spread the love.
Use a credit card or Paypal "regular" payment. It's much more difficult to dispute a charge on a debit card and a Paypal donation is gone forever.
Buy from sponsors/members of this forum. If they screw up, we can all go after them.
Example.