Depends, do you know anything about forestry and timber harvesting? Do you know the value of the wood you're sitting on? At 40% to the logger, and its all a junk pulpwood thinning, yeah, a pretty good deal. If its roadside veneer clearcut, not a good deal.
You need a contract, and a management vision, forestry wise (type of harvest, regeneration plans, etc). All aspects of the job must be defined therein. A perfromance bond and shut down clause can protect you if the logger is not fulfilling the contact during the job. Start with fulfillment of logging Best Management Practices and a visit with university extrension forester or state forester.
I've cut for guys (unfortunately) who sold themselves to landowners as "low impact" and got 60% for it, then high graded the hell out of the timber. Sure, it still looked like a forest to an untrained eye, (minus all the debris, etc typical) but it had nothing but supressed trees left, whips. he did not educate the landowner,a nd provided a disservice.
If this dude is knocking on your door looking for timber, be a little wary. Feel free to define the situation, ask more questions.