If imitation is the sincerest form of flattery, then InstaTrim owner Greg Amundson wishes his business wasn’t so admired. Over a decade, his made-in-Minnesota sealant grew to more than $3 million in sales last year. But this year, sales are down by 35{8ba6a1175a1c659bbdaa9a04b06717769bcea92c0fdf198d429188ebbca09471}. Amundson and his lawyer attribute the abrupt decline to patent-infringing counterfeiters, mostly Chinese, who have launched about 30 similar products over the last several months on Amazon.com. InstaTrim had been relying on the e-commerce platform for about 80{8ba6a1175a1c659bbdaa9a04b06717769bcea92c0fdf198d429188ebbca09471} of its sales. “It’s amazing how fast the counterfeiters are eroding our sales with look-alike, copycat products,” Amundson said last week. “If you search Amazon for ‘flex-trim’ and ‘caulk…