We are renovating our 70's cedar clad pole house. My husband painted between the ceiling beams in the kitchen/dining/living open space. He has just finished laying parquetry on the floor. We felt it was in keeping with the wood but felt the ceiling needed lightening up. It definitely brightened the place. I love it. I also sprayed some light fittings that were green fake verdigris with white paint. That also updated without detracting from the retro feel. Our kitchen has cupboards painted white and some drawer fronts in a wood finish.

We recently updated an apartment to sell and got great feedback from the buyers on the paint - Dulux 1/4 Lexicon low sheen on walls and Vivid White high gloss on doors, picture rails and trims.

I agree with both your painter and your Google result. The issue is something that has soaked into the surface of the old wall, particularly as you had an odd result when cleaning. You can’t expect the painter to sand and paint as part of the original job but they may be able to offer advice and action if you’re prepared to pay them. If you want to DIY I’d be sanding the wall and trying some stain locker undercoat.

quite possibly, that was going to be my next solution! heading back there in a moment to check it out. the existing tiles have been layed quite nicely/flat so i dont think tiling over would be an issue