Its pretty item specific.
Releases, sights, stabilizers, and quivers etc.. are pretty safe, just use common sense.
Arrows. A lot depends on your refurbish ability, can you build your own? If so then they can be a deal. I know when I sell arrows I try to include them in a bow sale, or intentionally sell them stupid cheap, because they can be so personalized and condition can be tough to determine from a visual inspection.
For bows..... Do your own research to confirm the bow will work for you before even contacting the seller. Lots of horror stories of the "great deal" that turned out to be money wasted on a bow that couldn't be fit to the shooter correctly. Once you know the bow is something you want and will work for you. Ask if its ever been dry fired, if they say no proceed, your relying on their honesty regardless. If they say yes, +1 for honesty. Get the details and proceed with caution, dry fires are not the kiss of death, think of it like a rebuilt title on a car. If they say "what's that?" walk away.
Broadheads. If wanting to try some new ones they can be a cheaper way to go especially if you can find some used to test drive before a new purchase.
Rests. Buy new.