1 ACCEPTED SOLUTION
Accepted Solutions
You have no obligation to meet the buyer's demand, as you're right that this sort of thing needs to be discussed and arranged prior to the sale (well, technically, it can still be discussed and agreed post-sale, but very few sellers are inclined to agree to additional costs without the opportunity to account for those costs).
Is it the same buyer? There are quite a few who have a standard message they send to all sellers. eg I once had something listed as B-grade and explained that the items had some oxidisation that was visible, along with suggestions on removing it if desired.'
Had a buyer purchase some and leave a note with the order telling me to pick out the best ones to send and making sure they were all in perfect condition etc. I messaged them and explained my listing to them directly, and their reply was to say they sent that message to sellers with every single order. 
(This is just one of the reasons I removed the option for buyers to leave a note with their order. People think it's ok to make demands or leave instructions that normally you'd need to ask / pay for).
Anyway, I digress a bit... 
I send buyers like this a message, stating that I can accomodate their request for $x additional, which can be arranged through a custom listing that they can purchase. I then advise that since they had made a special request, I am unable to post their item according to their specifications unless and until the additional purchase and payment is made, so if they would prefer the order be cancelled instead, to please let me know. I also state that (because I am obliged to post items within my handling time) if I can not confirm their preference by X date (last day of my handling time) the order will be automatically cancelled (I always follow through on this, too).
This message makes them get in contact, or makes them passively agree to cancellation if they don't reply. If they reply, you will be able to gauge whether they are being unreasonable and demanding something they are not entitled to (and have a record accessible by eBay of that), or if they'll recognise that they need to pay for what they want and either cough up the funds, or advise you to send normally, which again gives you a record of them agreeing to the services offered. It puts the ball in their court, and provides you with options when the buyer attempts to dictate their own.
Most of the time buyers message back and just tell me to do what the original listing says etc, some never reply and I cancel their orders (selecting either buyer asked to cancel, since I take no reply as passive withdrawl, or something wrong with their address as the reason). Occasionally they'll pay extra for what they want. Never had anyone argue with me or insist on their terms 🙂
