Personally, I believe unless you are an actual EMPLOYEE of a company then you should be paid the lions share of whatever an event was booked at IF you are supplying your own equipment, and facilitating the event physically as a sub contractor
You supply the labor, equipment, time, transportation, customer service/preparation, fuel. If YOU as the DJ have to also spend time to sell yourself to the client in order to get it booked this should equate to a higher percentage of the booking.
They supply the lead, and agreement. IF they did the selling, and also booked the client 100% themselves without any help from you, then they should be acquiring more of a percentage of the sale.
An Outlier. Are they supplying the insurance coverage for the event, or are you as the DJ having to use your own insurance too? If they are, a little more goes to them. If you are required to have your own, or use your own...more should go to you.
If you are supplying everything, and all they do is filter a lead your way, and handle the agreement with the client along with collecting the money. I certainly wouldn't be happy with them charging Double or more what I am earning by doing literally everything else.