Maybe the seller is in no hurry to sell and is seeing if it is worth the price they are trying by anyone.
This sort of thing is precisely the thing I dislike, needing to have an instinct on what might be accepted and what not. It's all a gamble whatever you choose.
Maybe they've done something up which they think is worth £7k to get back ?
Fund it himself, back out of the deal, or put in a lower offer pleading an inability to get that size mortgage. That seems to be the three options.
And I'd concur the £7k is a small percentage of the total price, so it may just be a case of pride in avoiding being persuaded to pay over the odds, rather than any real reason not to go ahead. Good luck whatever is chosen.