This is part of the prospecting that goes on when either buying timber (procurement forester) or as consultants. I've done it both ways.
Names are gotten off of tax maps. We used to routinely go through the tax maps and get every landowners name with 25 acres and up in woodland. Then we would get their mailing address. Then shoot off a letter. This was done during rainy, snowy or muddy times of the year.
As a consultant, we would send out "newsletters". We provided lots of information. It was more of an advertisement. We would get about 2-3 responses per thousand mailings.
If we were marking an adjoining woodlot, we would normally send a letter to all the adjoiners, advising of the sale and to make sure that there were no questionable trees marked. Of course, we would gladly look at their timber as well.
On occassions, I would send a letter to a landowner that had marketable timber. Usually these were landowners that were absentee. Response rate was relatively low. For the best response, personal visits are always the best. I was only run off once.
The guy who wrote you the letter may not know whether you have marketable timber or not. Just prospecting, but now he has your interest. Pretty good for a small investment of time on his part.
Whatever you do, make sure you get at least on other opinion. Same goes for price. Check references. Check markets - things have been off lately. Market timing is everything.