Depending on who you buy from, you will get vastly different prices and guarantees:
At the high end of the range are dealers who sell guaranteed (usually calibrated) lab grade test equipment at a (substantial) fraction of the new price. Their web sites are probably most interesting for the information that they have about particular items, since some of the cut-rate guys only say something like “HP200CD”.
Tucker is a good resource for identifying items and getting a sense of value. It has a large inventory with pictures and brief descriptions. If you compare to low-price equipment dealers, you will find that Tucker/3 is usually a reasonable price, Tucker/5 good and Tucker/10 a steal. I haven't followed this market much recently, so this information may be out of date.
In the middle are dealers that have a 30day guarantee of operation but no calibration.
At the bottom end are dealers who sell stuff “no DOA” or “as is”. Many sellers have a 5 or 10 day “right of return”, where you can send it back for a refund, but are out the shipping costs. eBay sales usually fall in this category. “no DOA” means “not Dead On Arrival”, and doesn't have any clear legal definition, so it's really between you and the seller. This probably means that there's no obvious damage, lights came on when powered up, and there was no smoke. The key question is who pays shipping if when it arrives, you decide it is “DOA”.
I've bought most of my instruments on eBay. If you don't want to spend a lot of money, and are willing to take the risk of getting something that doesn't work, eBay is best (see my eBay hints.) Most dealers now use eBay for selling items with weak demand or that are more popular with hams and audio buffs than engineers. Because of this an astonishing thing happened: I bought a Tektronix 7A13 from Tucker, the premier over-price dealer.
If it's important to get something that works because you don't have the repair skills, then by all means, buy something that is sold as working. This is a good approach when starting a home shop because you can't repair anything without some working instruments. And once you do start servicing instruments, you'll find you need more instruments…
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