The reason you are getting three different answers is likely because it’s legally unclear or new grounds. The harsh reality is that you probably won’t know if you can get away with calling a marketing company until you do so and see how the HMRC reacts.
If you go for calling it a marketing company (or a services company), make sure you set up paperwork, procedures, and policies to structure the company as one. Go the whole mile. Half-hearted efforts are a leading cause of tax non-compliance.
That said, I don’t think a marketing company could reasonably collect rent. I can’t really think of any comparable situations where a marketing company collects or holds funds on behalf of the entity for which it is marketing. It’s likely at that point the HMRC would throw out your marketing claims. Taking payment could be construed as rendering the service since the service is rendered on condition of payment.