A lot of modded computers sell on ebay. I understand the learyness of buyers though. If you plan to sell them on ebay, use a reserve price. Also, let the customers know that you know what you are doing. Give them the ability to ask questions. A DOA warrenty and one week return for money back also builds confidence. Sometimes people want modded computers/parts but are uneasy about doing it themselves. Give it a shot!
-maestro