A seller added P&P onto my invoice after the sale, is this allowed?
Some sellers, for various reasons will try to add an extra charge onto your invoice after you've won an auction. Maybe they miscalculated the price or the item sold for less than they hoped, or they may be trying to get round eBay's recent policy of introducing capped P&P charges in certain categories.
Whatever the reason, it's not allowed, all costs must be stated up front and they're not allowed to add on an extra charge for postage afterwards. The only exception to this if you live in an area where couriers charge a surcharge, such as the Highlands of Scotland. Even if this is the case, the seller must state up front in the listing that some areas require a surcharge.
So what can you do? You can just pay the original amount and tell the seller that they aren't allowed to charge extra postage after the sale has ended, this will be enough in some cases. If the seller insists on trying to make you pay more, you should Report the Seller to eBay
Non Performing Seller
, if a few people do this, the seller will face sanctions and will eventually be suspended from selling on eBay.
Don't be afraid to leave negative or neutral feedback for sellers that refuse to honour a sale, as they can't leave you bad feedback in retaliation.