as long as there is no uneven wear (like your car is lowered,so your tires wear on the inside) then your fine. The main reason for "directional" tires is mainly for the water ducts. On directional tires,the water ducts are a certain patern,usually driving water from the center of the tire,to the outside. When they are on backwards,in rain,it would be driving water from the outside of the tire,in twards the middle. bad because obviously water being driven to the middle of the tire will increase the chance of hydro plane. Other then that your fine,go back and get the shop that did your tires to fix his mistake.