not much need to rely on the seller. just do a bit of homework on what you need to look out for and draw your own conclusions.
ultimately, just find what you want then check for damage and wear. cracks and dents, more so cracks, are things you need to consider which can make a bike a write off only good for parts. dents are a shame and often won't be a big problem but you'll need to keep an eye on it. for what its worth though, cracks don't turn up that often on bikes for sale without people mentioning it.
then worn out parts are the next thing to worry about, only in so far as if they're completely worn they will need replacement, so just factor that in.
if you're going to pass it to a bike shop to do the work though, just get a new bike, probably wouldn't work out any cheaper unless you do it yourself. in which case it will cost barely anything
spotting thing stuff is pretty easy, its not specialist knowledge.
good thing about secondhand bikes is that you can get a hell of a lot for your money and theres a lot of interesting stuff out there within a modest budget. where as a lot of new stuff isnt that exotic or interesting (IMO) unless you spend loads
not much need to rely on the seller. just do a bit of homework on what you need to look out for and draw your own conclusions.
ultimately, just find what you want then check for damage and wear. cracks and dents, more so cracks, are things you need to consider which can make a bike a write off only good for parts. dents are a shame and often won't be a big problem but you'll need to keep an eye on it. for what its worth though, cracks don't turn up that often on bikes for sale without people mentioning it.
then worn out parts are the next thing to worry about, only in so far as if they're completely worn they will need replacement, so just factor that in.
if you're going to pass it to a bike shop to do the work though, just get a new bike, probably wouldn't work out any cheaper unless you do it yourself. in which case it will cost barely anything
spotting thing stuff is pretty easy, its not specialist knowledge.
good thing about secondhand bikes is that you can get a hell of a lot for your money and theres a lot of interesting stuff out there within a modest budget. where as a lot of new stuff isnt that exotic or interesting (IMO) unless you spend loads