I note that, halfway down your post, you actually agree with what I said - that the burden of proof lies with the OP. However, you have an overly optimistic view as to the proof required.
you are being ridiculous.
I do agree with the fact that the burden of proof after 6 months is on the purchaser because it's the law. I really don't have an overly optimistic view of the burden of proof at all.
If you had a small claims case on these facts and you asked the court for permission for an expert, the Judge would laugh in your face.
However, since the retailer is arguing that it is due to OP's misuse, she needs an expert report to show why it came off after a year
No she doesn't. Her own account of why/how/circumstances it came off together with photographs showing that it is not otherwised damaged will do.
If it came to it, OP can give oral evidence of the use of the furniture and it's a fucking piece of furniture not a Dale Chiluly glass sculpture. Furniture is expected to be relatively robust. Unless you are using a bed as a trampoline every day or setting about it with an axe, it should last a year and you don't need an expert to tell you that.
The sellers are trying it on with the OP and they know it.
The shit standard of advice on MN is eyewatering really. Why you would be encouraging someone to spend money on "an expert" for a piece of furniture that will almost certainly be less value than the cost of "an expert" at a point where they haven't exhausted all options with the seller is anyone's guess. Plus those costs wouldn't be recoverable in Small claims anyway.
If it's a modern version of a handcrafted Chippendale worth £££ AND you are at the point of having to issue proceedings, then it might be worth considering expert evidence but really not here and not at this stage.
What's the value of it @ImCamembertTheBigCheese ?
This isn't complicated stuff.