For right or wrong there are definitely some big spenders who seem more comfortable dealing with Vectis rather than ebay. We all know and have dealt with knobheads on ebay so maybe the premium is to deal with Vectis, but know what you're paying for/that it will be shipped properly/that it's legit/that you won't get scammed etc.
Most of us would think twice about spending big on ebay with a seller you don't know or trust, but I suspect we'd all spend that money with Vectis because it's going to be a transaction that goes well (despite the added cost).
There are celebs and rich people who collect Star Wars. It's difficult to see them wading through ebay listings like we all do, but they'd probably be very happy reading an auction catalogue and then buying from them. It's a shame for us "normal" collectors, but money rules.