It sounds like you’re looking for reassurance so let me offer that to you.
I’ve sold a lot of high value items, in a few instances hifi equipment that sold for £2000 for a single unit, and sent it courier without any problems.
The website Parcel2Go is your friend here as it lets you access commercial courier companies with ease and you have lots of choice to have the item collected from your home or dropped off at a collection point. I’ve done both and now default to dropping the item off at a local collection point (a newsagents round the corner).
As long as you do the deal inside of eBay and Paypal and you upload the tracking number you have nothing to worry about. I would even strongly recommend you open up the auction internationally as this will give you between 15% and 20% more on the sale price especially as sterling is so weak.
I recently shipped a pair of carbon road wheels to California without issue for instance.
Get a frame bos from you LBS (they are always looking to get rid of them) and buy them a beer to say thankyou. Then pack it up really well. You really don’t have anything to worry about.