Looking at other similar cars I don't think their price is unreasonable for a main dealer but as far as I can make out but Heartys are only a used car dealer which makes it a tad expensive given the mileage. That said the market is still recovering from Covid and iprices are all over the place. Selling prices are low whilst forecourt prices remain high, so if the car has been on their books for 18mths then my guess is there may be very little room for negotiation, unless of course they just want rid of it. Ask for £500 off perhaps? Will they include an extended warranty? ( something they can pass any potential profit on hence reducing the cars price for not a lot of money ).
The SE-L comes with a variable boot floor. The pics have it in it's lowest position - make sure it can fold up to it's highest postion ( creating a level boot floor ) and that it isn't broken. Pay particular attention to the leather - make sure there are no tears. And make sure everything works - that might take a while as there are several extras. The text says the car comes with personalisation. I can't quite make out from the photos, but if it does then make sure the car comes with three keys rather than two. I think I can just see the top of the third key behind their green ID tag on the keyring, but best check. That car clearly has adaptive cruise control rather than just ordinary cruise control as per their specs. Make sure it works 100%. Same with the heated windscreen. The car looks to also have the heated steering wheel - make sure it works. ( it could be a long test drive ).
If the car was ex-fleet then the interior may show signs of neglect in places but at least the service history should be intact.
My concerns? Both my Octavia and Karoq came with full leather and both were very well looked after. When I sell my cars, they're almost perfect, not far off showroom condition. That said I'm the first to admit that the leather Skoda uses isn't the best quality / fitment. Within a few thousand miles, the leather on both cars had a tendancy to sag / looks a little loose - looks like it needs stretching. The side bolsters on leather seats are man-made leather, as is the leather on normal SEL alcantara/leather seats. Even within a few thousand miles you'll start seeing creasing, it's unavoildable. I know it's only a picture, but those seats do not look four years / 50,000 miles old - they look almost brand new to me. It's defo worth looking for signs of wear around the cabin. It's one of those weird situations where if it's too good to be true... especially from an ex-fleet car.
As I say my car was an April 2017 car which I bought it for £18,000 and sold August 2020 for £13k direct to a Skoda dealer, a price which I was very happy with compared to other offers I received at the time. They put it up for sale at £16k which I thought that was a bit cheeky ( it was one of the most expensive Octavias advertised on Skoda used cars ) and expected it to be sitting there for ages. Don't know what it actually sold for but it sat on their forecourt for no more than a week. You say the above car has been sitting around for 18mth? I find that hard to believe, especially given the extras. Their sales team can't be very good at their job if it's true
They say the car has autodimming door mirrors. I was under the impression autodimming rear door mirrors could only be specified on SE-L if another option was selected - it may have been electric seats, Of course that was back in 2017, the 2019 specs may well have changed by then. Someone with a model of that era would be able to confirm. If it does come with those autodimming mirrors, pay attention that they're working correctly because it's a part of the car that's prone to accident damage and they're expensive to replace. In normal daylight they should look like they're tinted, but the view is clear. A damaged one may not show signs of cracks, but the view won't be clear.
Hope that helps.