It is not allowed to withhold the selling price in the MLS. If your seller wants you to not publish the sale price in the MLS, call thge MLS for instructions. You or the seller may be charge a fine for not stating the the true price. The MLS will change your incorrect price to the public records sale price when the prices goes to public records. So tell your seller the sale price will not remain a secret very long. The reason your MLS is updating the information is obvious – agents need comps!