The cost (your time x your salary) of searching for new suppliers. Basically no cost, we are free! We get paid from the sales and marketing budget of any supplier (as if we worked directly for them). So, at worst you get the same trade pricing as if you went directly to them, quite often we can squeeze a bit more discount!
They may have a great web site but how do they perform? If you were to complete the same checks as we do just imagine the cost to your company! Where is the financial check we hear you say, well this is ongoing and should be done before most orders. We will monitor this and find a new supplier if we feel there are problems - but even credit checking agencies can get this wrong.