With the price of diesel fuel (trucking) what it is it doesn't surprise me that some renders are starting to charge for picking up grease. I've heard they have also starting to charge for picking up dead stock.
One of the things that can come into play here is that the person you make an agreement with might not be aware of contractual agreements with a renderer. This is especially true with national chains. There is also the chance that the person that says it's OK to pick up grease may not have the authority to do so.
A lot of the sensitivity that renderers have has been brought on by a perception that their raw products (restaurant grease, dead stock, shop-fat and bone (butcher shop trimmings), and even offal have very little or no value. In reality, to the renderer these are all valuable commodities --- so valuable that they wait in line for years for permits to build multi million dollar plants to process the material for resale.
In the past, fly-by-night collectors have raided bins and barrels and either sold the material as is to competitor renders or, partially processed it so it would be more valuable and easier to sell. I think I mentioned it earlier, this creates a hell of a clean up mess when the fly-by-nighter elects to pull up stakes and move on. Because of the perception that the product isn't worth anything the employees at the location being raided seldom felt there was anything wrong with the raiding. In some states this got so bad that laws were passed to require there be permits to haul grease and animal parts.
I'm no attorney but my personal opinion is that even if the render is charging to pick up the product from a specific location there is a contract and the contract is for all the material. I'll bet that the fine print of the contract says "we guarantee to pick up all your material and you guarantee to supply us with all your material. I'll further bet the rate that is paid per 100 rate is based on receiving a cetain amount of material. The more the renderer receives the less the restaurant has to pay per 100 wt. This practice helps offset the price of trucking AND locks the market.
What many restaurants, butcher shops, feedlots, county governments etc don't take into consideration is that the renderer doesn't have to pick up anything unless they have a contract. This was made evident to California officials that were giving one of my old customers a hard time about the odor from dead stock they were processing (recycling) in the summer. They threatened to sue the renderer over the odor so to solve the problem the rendered stopped picking up dead stock. Within two weeks the farmers and feed lots had a problem. There were hundreds of head of summer deadstock needing immediate attention. While not as severe, a render can refuse to service a restaurant. When that happens the restaurant has a problem. If they can't find someone to pickup ALL their material. They could lose their license.
Please understand --- I'm not anti bio-diesel home brewer. I also know that this is frustrating. The only reason that I've gone into so much detail in this is so you can understand where the commercial collector is coming from.
The company I worked for (sold for) is a world leader in bio-diesel processing equipment. Many of the renderers, either directly or indirectly, are doing the same thing you are doing. They are just doing it on a much larger scale and they have jumped through all the hoops for licensing and processing (renderers are licensed) policing. It's big business.
Having said all this, no doubt there are restaurants that renderers aren't servicing or don't have under contract.