A note on wire size. You may find a radio that includes a wire harness. If the harness is complete and uncut it can save significant time and money during installation. If the harness was used in a 24 volt system and you plan on installing in a 12 volt system be sure to verify that the wire gauge is safe to use in a 12 volt aircraft. One advantage of 24 volt systems is that smaller diameter wire can be used. 12 volt systems on the other hand, generally must use larger wires to supply power to the same radio. This is more of an issue with newer avionics that are designed to operate over a wide voltage range, typically 10 to 30 volts. This pdf document on the Blue Mountain Avionics site is a good source of information on aircraft wiring.

Some sellers offer a Dead On Arrival (DOA) guarantee. This means the seller is confident the item will not be dead when you get it. Other items are sold with a bench test guarantee. This means the item is guaranteed to bench test OK but not guaranteed to work in your aircraft. Sellers do this because many times radios are removed as defective when the real problem is related to antenna or wiring issues.

eBay offers buyer protection for some items, to learn more visit:
http://pages.ebay.com/help/buy/protection-programs.html

It is common for the majority of bids to be placed during the last few minutes of an auction and for the price to rise significantly. When you bid and enter a maximum price for an item, eBay will automatically rebid for you up to your maximum price when other bids are made.

Make sure to ask the seller about boxing and shipping. Avionics should be shipped in large boxes with a minimum of 4 inches of foam surrounding the radio. It is especially important that indicators and any instrument with a needle movement be double boxed. The inner box for an instrument should provide at least 4 inches of foam, the outer box should provide another 4 inches of shipping peanuts or comparable material. Indicators should always be shipped solo and never in the same box with a Nav/Com/GPS. All avionics shipping boxes should then be marked as "Fragile". The extra $15 you'll spend to ship this way is one of the best things you can do to insure your purchase.

After the transaction is complete be sure to leave feedback. Feedback for buyers is usually expected when the buyer pays. Feedback for sellers is generally left when the item arrives and is verified to be as represented.

If you have a problem with the transaction try to keep your correspondance courteous and factual. Avoid the use of all CAPS in email, which is considered YELLING. Most problems are resolved quickly and amicably.

Fraud Alert! While the vast majority of sellers offering avionics are honest people, there are as few scam artist working the avionics listings. They are usually attracted to popular and expensive items like the GNS 530, 430 and GPS 396. Many times the listings will not have a gallery image and will be posted in a non-aviation category. Recently we noticed a GNS 530 being offered in the ladies shoes category. There was no gallery image and the "seller" claimed to have 3 for sale at $2500 each. The scammer also asked buyers to contact him via email and to not bid using the standard eBay auction process. Never wire funds directly to an offshore account.

Fraudsters will gain access to legitimate accounts using spoof emails. Make sure you understand what a spoof email is and how to avoid becoming a phishing victim. Take some time to read the eBay spoof tutorial.

This page on craigslist contains helpful information on avoiding on-line seller scams.

Good luck with your search.
-AvionicsList.com