Sorry but you are in a no win situation. *If the machines cant be inspected in working condition ( ie turned On & used) there is precious little you can check.
To answer your other questions. Nothing wrong with a Bo-Ema machine. Just like everything else, if you specify the correct equipment for the application, it will do the job. When in good condition and set up properly, Bo-Emas work well. As you do not know the model, it is hard to say whether they will be small volume machines or medium volume machines (or high volume).
That said the coffee made from a Bo-Ema in good working condition ( commercial HX) *cant help but be a trillion times better than that made by any small (domestic) machine, which is what you are asking I believe.
When you inspect, take the lid off (if you can...suggest you take a normal and a phillips head screw driver although in most ccases the top plate screws have been lost years ago...).
Look at the way the groups are fitted to the machine. If the groups are bolted to the chassis, and from there, individual copper pipes run to the boiler, then the machines may be worth picking up at the right price.
If the groups are actually welded solid to the boiler...walk away. This type of Bo-Ema is older than Noahs ark and due to the groups actually being part of the boiler, they run far too hot and burn coffee to your hearts delight.
Note older Bo_Emas do not enjoy the same quality of build as their european counterparts. Buying an old Boema is like buying a 15 yr old daihatsu charade..... Is this what you want? (apologies to old boema and daihatsu charade owners hehehe).
Newer Bo-Emas are quite nice small volume machines!
Be careful that reading what many coffee snobs get up to in their chosen hobby, doesnt influence you to take a bigger step than you can cope with.....you are a brave man frontig up to an auction to buy an old coffee machine.
Suggest a better way is to pay more but buy a tangible, working machine from someone, that doesnt need work, and enjoy the coffee.
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