Strata Management charging ‘advertising’ fees to contractors

Being quite new to providing trade services to strata buildings, I was a bit shocked when requested by the strata company to pay a monthly fee to be on their trade register.

They assert that this covers their time to put me on their register, check that I have appropriate insurance cover etc, advertise on my behalf on their website and arrange repairs for strata buildings.

I cannot opt out of the advertising because they will not give me any work if I am not on their register.

I recognise that there is time involved checking that I have the right license etc but this is an annual activity? With arrangement of repairs, isn't that what the strata management fees go towards and so, isn't this double dipping? 

I am told my fee (which is significant) will be reviewed annually and is based on volume of work – is this something that must be disclosed to the Owners corporation?

Is this legal/ethical/standard practice?