What does the flashing arrow mean on cars in the store that appears when you buy a duplicate card?

It means you can upgrade it to a higher level using Rubucks. Leveling up makes clothing and wigs better when it comes to challenges. You’ll have to buy 1 duplicate for common items, 2 for uncommon, 3 for rare, 4 for epic, and 5 for legendary- not counting the original you’ll need to purchase if you do not already have the item. Upgrading gives clothing better and a greater number of tags depending on the grade of the item.