Is the seller allowed to change the colour of an article won on a bid
No. The item must be as described. However, the buyer and seller may agree to a small change. For example, I recently had a buyer order US postage thinking it was Canadian. Since I had both in stock and they were the same price, we agreed to the change.
However, the buyer cannot demand the change and the seller cannot randomly make the change.
or to add another item to the order to save on shipping?
Most sellers will combine and discount shipping fees for multiple purchases. ASK before bidding if this is important to you. The seller is not required to do this.
If your seller is difficult about this you can leave feedback for up to 60 days. At that time you will also be asked to leave Detailed Seller Ratings, which are actually much more important. Two of the ratings are for Communication and for Shipping Cost. The normal rating for a normal transaction is Five Stars. The lowest rating is ONE Star.
