( decorator) Did a flat up last year, two smokers who never opened windows. It was grim,lk although the smell got improved once the windows were left open for a few days. We removed carpets, but left underlay, which was ok.
Walls, ceiling, and paintwork: thorough wash with sugar soap, and rinse. Wear protective clothing, gloves and masks - the yellow brown fluid running down was full of smoky nasties.
Every surface, inside of kitchen cupboards, everywhere.
The plaster walls and ceilings had so much smoke in them, that even after washing, it would change the colour of emulsion paint, so everything had to be painted white first, then with colours.
Sorry if this sounds grim- we got a good result, and it was satisfying to turn the property around. I'd buy similar, if the the price genuinely reflected the work involved.
But I wouldn't live in it, or move in, until the work has been done.
If I had an asthmatic DD, I would be sealing the walls of her bedroom with a sealant paint. Not difficult, but pricey - maybe £150, obviously depending on room size. Google third hand smoke, but don't get too alarmed - this can be sorted.
Oh, and when you wash the plaster, it will really release a smell - disappears as it dries, returns briefly when paint is wet.