Lawmakers were advised Tuesday on the pros, cons, and what researchers still don’t know about taxing marijuana. Beau Kilmer, a senior researcher for the RAND corporation and co-author of a major report contracted by the legislature last year, presented to the Senate Finance Committee. “Quite frankly, nobody knows the best way to tax marijuana,” Kilmer said. In theory Vermont is in a good spot, financially and geographically, to set up a legal pot market. With the closest legal market in Colorado, Kilmer said that within 200 miles of state lines — encompassing New York City, Boston and Montreal — there is a market for the drug that is 40 times the size of the market within Vermont’s borders.