Just attended a very informative and practical session at the Aviation Suppliers Association's annual conference on best practices for approving vendors.
Jimmy Wu, Infinity Air president, and Mitch Weinberg, International Aircraft Associates president, discussed things like due diligence, establishing an escrow (like the option you get for paying your home mortgage), bank and trade (which lays out things like payment terms and types, as well as verifying available bank funds), different types of insurance and cyber security.
"Don't be shy when buying," urges Weinberg, "and conversely, when you're selling, know your customer. If not, it goes against your bottom line."
That's good advice.