Yes. It all depends. I'll dumb it down and make it as boring as possible.
How it typically works is that you get an agreed rate to the client. Let's say it's $1,500 a day for your services. It's then on you, once that contract's been awarded, to try to find that resource. At that point, you negotiate their rate. If their rate is $1,000, you've now made 25%. If their rate is $1,200, you've now made x%. It all depends on what the negotiations are between what the rate is to the Crown and what the person you've found is charging. That delta in between is the margin.