It's a shame you have to sell your bike!
If you do want to sell it on ebay perhaps you should put a reserve price a little higher than those 700£ and maybe add a Best Offer button... who knows, you might have a better offer
Btw, It is possible for a 20+ year old bike have very low mileage..
before I started using my '90 XT600E my dad had bought it in the US it only had about 2500miles on it.
That was 16 or 17 years ago and until I started riding her just a few years ago it only 4500 miles....
The bike sat in the garage and he only rode it in the summers... but hey, what can i say, lucky me
And if I recon, it has a little over 19000 great awesome fun miles on the clock