Ebay have no idea what you actually sent, or what condition it was in when sent or received, as they were not present when sent or received, so have no choice but to accept a buyer's word for it when they claim Not As Described, as per their Money Back Guarantee. They cannot get into disputes between you and a buyer. Only a judge can decide if a buyer is a liar or scammer.
You agreed to comply with the MBG when you registered your account. If you dig your heels in and refuse to offer refund on return, Ebay will either force you to pay for a returns label, or they will force the refund without the need for return. You will also have a damaging defect slapped on your account for failing to comply.
This may sound unfair, but it's the fairest it can possibly be. The MBG is a very good thing (although you may not think that at present) as it gives buyers the confidence to shop with you and every other Ebay seller. Without it, you'd be lucky to sell anything at all. In fact, without it, Ebay would no longer exist.
If the buyer opens a case, you will have to agree to refund on receipt if you want the plants back, or refund without the need for return. That will at least get the Ebay selling fee credited back to your Ebay account. And then (if you're 100% sure that the buyer is being dishonest) report the buyer to Ebay for abusing the MBG by fraudulently claiming Not As Described (via the 'report' button on your ‘leave feedback’ page). A few of those from different sellers, and their account will soon be toast. And add their Ebay ID and PayPal email address to your Blocked Bidders List so they can’t darken your doorway again.
You can then deal with the buyer outside of Ebay as follows if you wish (and if you're absolutely sure the plants could not possibly have arrived in that condition, or were not infected with a plant disease that could have caused this rapid decline):
Send them a PayPal invoice to cover your losses, giving them 7 days to send cleared payment or you will be taking legal action and reporting them to Action Fraud (the police's online fraud unit).
If payment is not received within that timeframe, send them a 'before action' letter by Signed For post, giving them 7 days from receipt to make full and cleared payment, or you will report them to Action Fraud, and take them to Small Claims court to recover your money and all court and other costs.
If payment is still not received (unlikely, as this is generally enough to put the fear of god into small-time fraudsters), take them to Small Claims court if you wish. Very easy to do, and the process can be started online.
@5265jill
