A convenience-store chain is challenging Iowa’s spot-checks of tobacco sales.The Kwik Shop near downtown Ames was cited by the city council for selling a tobacco product to a minor during a police spot-check. It’s become routine for law enforcement to pay periodic visits to retailers using a mature-looking teenage volunteer, to see if clerks will ask for ID or refuse to sell tobacco to an underage buyer. Lawyers for the Hutchinson, Kansas-based Kwik Shop chain say the city was arbitrary in fining the store after its worker was found guilty of selling to a minor. The state law says a civil penalty will be assessed against a store that sells to kids, but the Des Moines attorneys suing on behalf of Kwik Shop say the state’s law is unconstitutional.