Banned
Yes I have had this with a major IT company
Not a problem at all as rate and conditions were all agreed with end client before agency came in. It helped also a lot to get paid within a week after invoicing in stead of waiting the 90 days that they normally use
More time posting than coding
Like others have said, assuming they're reputable, I'd probably prefer dealing with the agency as they'll agree to resonable payment terms. Bare in mind you've already agreed the rate, so it's not like the middle man is costing you anything.
Godlike
Just make sure there aren't any stupid handcuff clauses in the contract. You brought the business to the agency, not the other way round.
That goes double if the client is a large multinational: you may well get another contract with another branch of the client and there is no reason to be tied to that agency for the future.
Double Godlike!
Have they pushed you to a particular agency or do they have a PSL for you to choose from?
The greatest trick the devil ever pulled was convincing the world that he didn't exist
Banned
One reason would be that the client will most likely (IME anyway) not have a suitable contract to use so you will be able to put forward your own terms based on the PCG or QDOS's contracts. The payment terms don't matter so much if the warchest is up to scratch and there is an overall reduced risk due to the better contract and fewer parties in the chain who could go bust.
Boo
Double Godlike!
Just did mine on Purchase Orders rather than contracts when I did it.
Banned
Those are not mutually exclusive as it is commong for a PO to reference a contract number.
I personally would rather have a few things spelled out so would not accept a bare PO, expecially as it will have the client's standard terms and conditions on the back which will be a) extremely disadvantageous to YourCo and b) almost entirely irrelevant to contract roles.
Boo
Double Godlike!