Plastering - can anyone advise?

[Renovirgin2018]

We have recently bought a 1930s semi and the time has come to get quotes in. Following advice we have asked 3 plasterers in. Plasterer one said - Even though it's a small room (box room, not much bigger than a double bed) there is a lot of blown plaster. He will dig it out and repair it, making sure all the walls are perfect. He will guarantee the work and it will cost £600. Plasterer 2 said - Blown plaster doesn't matter, all houses have it, will just skim it over. £400. Plasterer 3 is coming today.

Obviously we want to pay as little as possible but who is right? Is plasterer 1 just trying to justify his price or will plasterer 2 leave us needing to redo the job in a few years?

Can anyone advise?

Will plasterer 2 guarantee how long it will last?
If not - plasterer 1!

I wouldn't get plasterer 2 back!

Skimming over blown plaster is a terrible idea. It will look nice for months/years but as soon as there is any vibration through the house or with time it will crack, and could then pull all the rest off with it.

£200 extra to take off old plaster, patch then skim is good value, especially if there is a lot to do, and a guarantee is priceless.

Had to edit this post as it isn't necessarily blown plaster. They both called them hollow spots - not sure if that's the same thing???

Both plasterers are talking about repairing what is there.
The ‘correct’ way is remove the skirting and architrave around the door.
Hack off all the plaster back to the brickwork.
Add any more power sockets.
If the house is not insulated, use insulated platerboard on any external walls, normal plaster on internals, then skim the lot, refit or replace the woodwork.
It’s going to cost more than £600 to do that.
If you don’t fancy going the whole hog, plasterer 1 then. But he will only hack off the hollow spots, wet the wall and refill it, then still skim over the old and new.