How/what to check when purchasing used speaker cabinets?

I am looking at purchasing two different cabs...One is a 1979 Marshall 4x12 w/ Marshall labeled G12-65's small check grill cloth-
The other I think is a 1978 Marshall with painted over grill cloth? and G12M -75hz blackbacks..
I can see the frame codes-will be checking out the cone codes for possible re-coning and any tears...
I am a bit concerned that spray painting of the grill cloth may have got on the cones?
With it being wired up-could I measure the the ohms off the tip of a speaker cable?
Could I still use a 9v battery to check the speaker for possible rubbing?
Any tips are appreciated...

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