Would you accept a lower offer to avoid student tenants below?

How good is the sound proofing, do you share any communal areas or gardens etc? Do you have small children?

I'd accept a reasonable offer. I've just swapped an obnoxious single male neighbour for a group of students. I'm sure the students will be noisier, but I would be flabbergasted if they were as generally disruptive and unpleasant.

Can you do any research on how well-managed this potential buyer's rental properties tend to be?

That would give me pause for thought, but if his money's good... Spend some of it upgrading the soundproofing? Personally I'd much rather have noise underneath than overhead. I would also check the legal position re arrangements for the shared garden. Students will smoke or vape in it and might hog it in barbeque season.

There is no guarantee another buyer will be any better. Or that your hypothetical perfect buyer won't get a job abroad six months after moving in and let the flat rather than sell it - or sell it to a scumbag landlord...

No. Noise from neighbours is so stressful and 3 students are quite likely to be noisy. I’d exert as much control over the process as you can in terms of selling to the right buyer.

I wouldn't sell to someone who will let to 3 students if I was living next to them. It's completely different to letting to a couple.

Of course you may get 3 nice quiet students but you're quite likely to hear loud music, parties, lots of friends and visitors and they are likely to stay up late.

OTOH, each set of students is only likely to be there 9-12 months so if you get a nightmare lot you know you'll be shot of them in the summer, whereas a nightmare long term tenant could be there for years.

And students do sometimes respond to being told off - there are student houses in my street and neighbours have had words at times.

You don’t have to accept any offer, it’s your choice. Students in such close proximity would concern me. My DS lives in a ground floor student flat with his GF and it’s immaculate. I stay there regularly and they’re quiet, respectful and good neighbours. That’s not the norm. They’ve had 2 lads upstairs creating huge amounts of noise, mess and general chaos. I’ve been woken up in the early hours when they’ve come home and continued partying, they seemed to be nocturnal.
They’re hoping for better neighbours now they’ve moved out but it’s a lottery. Thankfully it’s only 9 months until their finals then they’re moving out.
I’d wait a bit longer if you can to avoid it being a student rental.

Flats are not selling well. It's unusual for your lease to not restrict occupation to a single household so it might be worth checking that. You could get 3 months into the process and lose the sale due to a restriction.

Check any restrictive covenants. A single family household should exclude a HMO that he’ll need a license for.. does he actually know what he’s doing!

By selling it at all, you obviously lose all control. Any neighbours can be considerate or awful to live near. Take the highest offer in good position. How annoyed would you feel if you sold for lower then that buyer resold to a student landlord a year down the line?