My wife bought some beef mince (ground beef) from a shop. It looked red.   When she fried it, it give off an aroma of vinegar. Is it spoiled? 
The smell indicates a safety problem. There is no reason to add vinegar to meat (unless you bought already marinated meat, but 1) marinating mince is so unusual, the chances of finding premarinated mince are against zero, and 2) this would have been declared on the label.   The likely source for the smell is bacterial fermentation. Many bacteria produce acetic acid as a waste product (this is how vinegars gets to smell like vinegar). While the vinegar producing bacteria usually colonize other types of food, and meat tends to support bacteria producing other odors (the ones known as rotting meat), strange things can happen, and this smell is a big red flag. Especially with mince meat, which supports much more bacterial growth than a slab of whole meat (bacteria live on the surface only, more surface=more bacteria).      it looked red    This doesn't matter. The color of meat is not a reliable indicator for food safety. First, meat exposed to air quickly gets an unappetizing shade of green or grey. Second, because customers are known to turn up their noses at greenish meat, butchers can just package it under a special atmosphere, or just bathe it in chemicals which prevent discoloration, so it always stays red. Third, while meat does indeed change its look when it rots, this happens rather late in the process. Gas production (smelly or not) will come much earlier, and you should discard it at that point.  