OK, let me throw this in here:
Products are 'supposed' to be evaluated/tested by a NRTL, such as UL, or others that are approved here in the USA
Do all 'products' have 'labels' to show the NRTL? Short answer is NO.
Cover plates for switches, receptacles, etc., are IMHO a 60/40 mix. Have I had any issues? As Greg said, if it looks 'good', it's not an issue. In order to see any label. the cover would have to be removed, as the NRTL label would be on the backside. (Who has time for that?)