Have the harvester pick the site as they would to see if this fits your needs. E.g. harvester get .42 per pound for salal. They get 50 pound per acre per year. Determine how volume will be certified. Slip from buyer showing poundage sold is best.
Weigh scale is good for large volumes.
Start with a 2 year lease with the option to increase after review. Use stewardship plan to obtain work instead of cash from harvesters. This promotes long term commitment on the part of both parties and develops trust. Set penalty for damage to non-target plants, roads, fences, equipment etc. Harvesters need to have insurance policy to protect you.