QUESTION re location shoot

I am many years shooting color nature photographs and making cards and
enlargements to sell wholesale and retail (privately and at shows). I was
approached twice last week at a craft fair asking if I would come to a
commercial property B&B and a private property to shoot for brochure shots
and the other just for vanity.
The question is, I have no idea how to charge for my time,
Do I charge per shot?
Do they get to keep the negs or just the prints?
Do they pay for the right to use the shots?
I probably would be more comfortable to only charge per useable shot since
ya know, everything is NOT really useable.

Your help in this situation is much appreciated.
Harriet.