I doubt the seller will offer that vacuum again at the same price. The seller has postage, return postage, and penalties to recoup.
I don't know why couriers don't validate postage before accepting parcels. They only need a set of handheld scales. Post Offices wouldn't allow it over the counter with insufficient postage paid.
It's not just eBay fees, PayPal fees, and Postage.
There's often Import Duties, Inspection Fees, Purchase/Value-Added Taxes.
Its a shame the "Marketplace" feature on here is so weak and under-used. It could have been a real alternative to eBay.
As you've been waiting so long for one of these; why wait for another 'bargain' to turn-up. Why not "bite the bullet" and pay the going rate for one now? You'll have the vacuum you've wanted for a long time, and can enjoy owning it for longer.