Find out who is allowed in before you shortlist
Some buildings permit any inducted and insured contractor. Others maintain an approved list, and a few require all cleaning to be done through the building's own provider. Each of those produces a very different comparison, and finding out which applies takes one enquiry. Gathering three proposals and then discovering that two of the providers cannot be engaged wastes everybody's time including yours and it removes providers you were never able to appoint anyway.
Where an approved list exists, ask how a provider gets onto it and how long that takes. Sometimes it is straightforward and a provider you prefer can be added within a few weeks. Sometimes it is effectively closed. Knowing which situation applies changes whether your comparison is between three providers or between the two the building will actually accept rather than one you assembled from names you found yourself.
