Some basic questions.
How did you come by the litho?
Do you know the name of any pevious owners?
Is the frame "old" and have you taken the print out of the frame? Some time there are notes on the reverse side as to who the original seller and buyer might have been. Is it matted? Go over the eges of the mat with a good magnifying glass if is a more recent reproduction it say so in VERY fine print. xyz publishing 19** Several of this type print were reproduced in the 1880's and '90's and if in good condition can fetch a couple of hundred $'s. 20th century repos are worth considerably less.
Lastly how does it smell? Does it smell old and musty?
Are there water stains or insect damage
What condition is it in? Is it faded.