It does rather depend on how much money we are talking about, and what services are included in your rent.
if you are benefiting from any front of house support, bookings, taking payments, dealing with enquiries, that’s worth quite a bit, especially if it’s available for more hours than you work. You also need to weigh up what the facilities are like. I’m a beauty therapist and for me, having a client arrive early creates issues if its a knock on my door and I’m interrupted, particularly if I’m talking to a client.
As a busy therapist I can rent my own place and run it with a part time receptionist for 40% of my takings. It’s a hassle though, you have to sign a lease which you can’t get out of for years and managing staff is quite time consuming and you get sucked into jobs that don’t really make your business grow.
I wouldn’t agree to a 40% deal if I was renting a room in a yoga studio, gym or wellness practice - I would go for it in an upmarket hair salon which had been successfully running for years.
Ultimately, if your costs not including products can be covered for £2k a month or less it’s probably a good deal. If you start to hand over more than £2,500 you need to renegotiate or consider getting your own place.
Bear in mind that a lot of commission deals are disguised employment. You are only properly self employed if you are taking a business risk that you might lose money. The risk needs to be more than the risk of not earning anything.