Whether it's a new airplane, new avionics or just putting your airplane into the shop for maintenance, know what the warranty covers.
You bought something and now it doesn't work. What recourse do you have? Can you compel the seller to exchange the bad something for a new one? If you return it, are you entitled to a refund of the full purchase price? Will the seller pay the full cost of getting it fixed? What if the something is three months old? A year? Five years? How long is the seller obligated to repair a defective product, exchange it or take it back and refund your money?