That is a worry, yes. I emailed them earlier to ask if their cleaning is optional or not. I'm still waiting for a reply - it takes a while since I merrily email in English
I guess it could be a standard thing that's done regardless. So, on the other side of the coin, I could still get in a company to do my move-out clean and the agency might insist on 'their' people coming in after (and me paying for it).
Afterthought (via edit): Or I could just pay their bill, try their cleaning and report back whether they inflate the costs. They shouldn't - I've no pets, don't smoke indoors, never cook - so there's no 'build up' from any of that.