Buying on ebay is frought, you take the risk.
Generally the used commercial ones are a safe bet, since they are built like tanks, but the postage on a 15kG beastie cost can somewhat reduce your bargain.
With used grinders I think you should also factor in having to replace the burr sets [$60-120], but otherwise if they are claimed to be operational they should be ok.
Obviously though, if the motor had burned or if the adjustment mechanisim has stripped/broken the grinder will be useless and probably too expensive to repair.
Also expect to have to completely strip down the grinder and clean it out.
However, If your bench space is limited a commercial unit is probably a no-go.
Watch the price for new/near-new grinders on ebay, in most cases they are basically at retail, so its better to go straight to one of our sitesponsors, get the right price and great backup.
The Rocky is a good starting point with a small footprint, but recent price rises render it less of a bargain.
Ascaso, Iberital challenge and Compaks could also be worth considering.
There are many "operational" differences between grinders and a site sponsor will be able to explain the various pros and cons and steer you towards the on best for your needs.
<======great advise can be found over here!
Personally, I wouldnt recommend starting with the sunbeam, it can produce great shots, but due to its build quality, it does so, with annoying un-repeatability.
So while you are carefully honing your technique, [especially if your introducing the extra variable of a lever machine] that grinder will be plaguing you with an inconsistant grind, ala bad shots.....That said, some seem to work ok and there are workarounds.