The most important issues when buying avionics are purchasing quality products and getting a quality installation. Call various avionics shops to seek repair history and failure rates on considered equipment whether you are buying new or used. These shops see this equipment on a daily basis and can provide valuable insight on the long-term effects of your purchase.

Rule #2 - WANTS vs. NEEDS: Is what you are considering a WANT or a NEED?

WANTS are limited by desire and money. If you want it and can afford it you should have it. NEEDS are driven by necessity and are more difficult to address especially if a limited budget is involved. In some cases, a blend between your wants and needs can be the most reliable and cost-effective avenue to pursue.

For example: If you are in need of a different reliable Nav/Com with Glideslope AND you want (or need) an approach certified GPS, for a fraction of additional cost, you may consider a new GPS/Nav/Com rather than a good used Nav/Com and a separate used approach GPS. The difference in cost will provide all new product with manufacturer warranty and can provide more user functionality.

Rule #3 - BUY BY APPLICATION

So much of today's options are driven by the type of aircraft, the capability of the pilot, and how the pilot intends on using the aircraft. This issue becomes most obvious when discussing GPS. I don't think you will find much argument if suggested that some form of GPS is almost a necessity. A VFR "weekend flyer" in a small single can obtain a high level of situational awareness (especially with the restricted airspaces) and value from a handheld GPS. A practicing IFR pilot who intends on tackling IMC conditions whenever possible (particularly in business applications) will rely heavily on an approach certified GPS. The choice of product, even in this realm, can vary between a GPS with a high level of intuitiveness but less overall capability and a GPS that requires a much higher level "learning-curve" but contains more potential operational applications. The point is this: You owe it to yourself to do some research and seek the advice of a knowledgeable "expert" to determine what will best suit your application now as well as any considerations for future applications.

No matter what you are buying, avionics purchases are not cheap. In most cases, you will probably require some installation work associated with your purchase. Your safest bet is to purchase your equipment from a respectable source because they are most apt to stand by what they sell. Keep in mind that many shops will not install equipment they didn't sell and/or may charge a higher labor rate to install such equipment.

Points to Consider

There are several points to consider when buying new or used equipment. They are as follows:

1. What kind of Warranty is associated with the product?
2. What kind of Lead-Time is required to obtain the product?
3. Are all components (antennas, racks, connectors, pin, etc.) included with the product?
4. What other accessories are required to install the product in your specific application?
5. Are there any subscriptions associated with the product?
6. What kind of service should be expected from the supplier providing warranty?
7. What is the long-term service forecast for the product?

The answers to these questions will put you well on your way to being an informed and pennywise consumer. For more detailed information, see:
How to Buy Avionics - Used
How to Buy Avionics - New