I'm in a similar position but as the seller.
I listed a loads of old stuff from my grandparents house clearance, we'd had a local antiques dealer round to check if anything was of value and he said no.
One particular item got a bit of interest, I'd put £5+ on the listing, this item was clearly the nicest and was going to be more, I thought maybe £20.
One person messaged asking if I'd post, I said no as lots of local interest, and he then sent me info that the item cost £2k new!
So I hastily withdrew it from sale and am now researching properly, which is a huge hassle as I just want the stuff gone and my spare room back, but since my gran is in a nursing home which is eating up all her savings, we need to get all the money we can. This item will pay for another few days of care at least!
I was very grateful indeed, I'm a busy working mum dealing with grandparents stuff and I don't have time to research everything, I thought the antique dealer would have spotted anything valuable, clearly he was a hack as this is quite distinctive and rare.
In your position I would just pocket the cash as a reward for my knowledge and hard work OP