Air mobility specialist Archer Aviation (NYSE:ACHR) saw its shares fall sharply, about 6%, despite a spate of positive developments. A manufacturer of electric vertical takeoff and landing (eVTOL) aircraft, Archer just came off better-than-expected results for the second quarter. Also, the company has inked credibility-boosting deals with major enterprises. Still, ACHR stock has printed red ink, likely due to valuation concerns.At first glance, the selloff appears irrational. Yesterday, Archer posted a loss ...