Craiglist...?

Okay I have a lot of people wanting to buy a computer i have for sell for 800.. everything mouse tower, keyboard 2.1 speaker and 17in LCD, and comes wit microsoft office 08, n win xp.. but i want to know how could i trust a buyer... like i know i shouldn't accept casheir check, but can i accept a certified check?, and should i trust someone with their own shipper?