Most everything comes down to the factors at play.
Is this item right in front of you at the time of purchase?
or
Large superb quality pictures?
or
tiny little fuzzy picture?
Price?
sometimes the price is soooooo cheap its worth the risk.
Why is the item being sold?
there are a multitude of reasons here, but i have come across a great deal of machinists that are selling off a LOT of the above mentioned items because they are retired by quite a few years, and will never use them again, or in some cases they are passed and the kids have no clue what the items are or how they are even used. Most of those guys took great care of the items and are still in perfect working condition, making some great deals to be had.
Unless of course you are in the LA area, then just pass on all of them