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Look for marks on the primary mirror - there should be nothing more than a little dust. No finger prints, no scratches. Use a torch for this, moving it about. DON'T do this with the scope pointing straight up!!! Tip down the scope for this. You don't want to accidentally drop something onto the primary mirror!!!!!
Same with the eyepieces, finder scope & filter.
Ask to see how the scope is put together for use, & how the main tube comes off the mount for transportation. Also place an EP in the focuser & move the scope about as if you were using it under the stars. All the actions should be smooth, including the winding in & out of the focuser.
Ask to see how to align the focuser - this will save you a lot of time.
Lastly, ask if the seller knows how to collimate (align) the scope's optics. This too will save you a lot of time & improve the quality of the image.
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