In the Trader's defence, he doesn't know what condition the kits are in (whether they're complete, started, part painted or factory fresh)
Which is exactly why my man is not keen on buying up collections, but if he does then it's a snap valuation of between £1.00-£2.00 per piece. Then the kits have to be transported and stored Iin itself an on-cost). Before re-sale they all have to be opened up to check for completeness, decals, instructions etc. In his case anything started or painted goes in the bin. I have every sympathy with the OP, but if he wants to maximise the value of the collection it's time to knuckle down, check the kits and get selling.