How much do you charge per LF for framing?

If you mean linear foot, the price is usually included in the moulding cost. If you are making a frame from someone else's moulding and you have to cut it and join it, I would charge just as much as a scratch order, since if anything goes wrong, you will have to reorder the moulding. This works out to 10 dollars per linear foot at cheapest to upwards of 50 dollars or more, depending on the moulding. If the frame is very small, you might consider a minimum charge. This of course does not include other materials, glass, mounting, hangers, and mats.