Owning your own home

It's not normal to try to sell integrated appliances (washing machine / dishwaher) is it?

Depends. Some sellers are just twats.

Usually there's some give and take in it. We bought the light fittings and curtains that our seller had listed (£500 on top of £££ is peanuts). But we declined the integrated appliances offer and they left them. They even left the massive fridge/freezer that wasn't even listed in the F&F; probably because getting it out of a 1st floor flat would be more effort than anything else.

I'm obviously not going to pay for them, but what should I be asking for to make it as unpalatable as possible for them to take it with them,

Just don't offer to buy them, if they leave them it's a bonus, no point requesting they be removed. If they do take them you deal with it when you move in (either buy something new or find something second hand).

Only state that something be removed if you really do not want it there. e.g. "Do you want to buy the manky dog hair covered corner settee in the living room for £2k?" -> "No, please ensure this is not left in the property."

integrated appliances are normally part of fixtures and fittings. They're included in the purchase price rather than something you haggle over after. standalone stuff fair enough for them to try and flog separately

for things that aren't fixtures and fittings - manky old sofa ^ for example then you can request they be removed (/they can offer to sell if you want them left)

for things that are, you should both expect that they would be included at no extra cost

Like anything it's worth a punt but in my experience the 'happy for them to be left but not willing to pay anything' pretty much always worked.