Teach me about Shipping Parts!!!

First of all, you have to be relatively comfortable with whom you are dealing with (whether it be a buyer or a seller). If you are buying or selling on ebay, you can try to get a handle on the buyer/seller by looking at their feedback. Since the feedback rules have changed recently, some may say it may be slightly eschewed but if they have been on there long enough, you can probably get an idea.

If you are dealing with someone on a forum, you can check out how long they have been on there, how active they are and possibly see what other items they have sold/bought on there. The people that have been around for awhile and participate regularly are usually trustworthy.

As far as payments go, it is customary for the buyer to send payment first and then the seller sends the part(s) out. As a seller (and if your comfort level isn't where it should be), you can request payment be made in a certain method (ie. postal money order) and then have the buyer send it via a service where you can track/confirm it (ie. Priority Mail w/Delivery Confirmation, etc.).

As a buyer, you have to feel comfortable with the description/pics that the the seller has supplied. Before sending the funds, determine what shipping method, confirmation and insurance you want placed on the package. Make sure that all responsibilities and expectations are understood by you and the seller. This makes for a much easier transaction (especially if there is a snag along the way like damage to the item).

I am sure others will chime in with other suggestions. Good luck.