Sanitary Transportation

Currently we are shipping bulk barley or oats and we have a transportation cleanliness form that we make sure the trucking company fills out with our staff filling out some of the information. It basically covers the trailer info, what was previously hauled, and then has a spot for whether or not the trailer was cleaned and by who. It has "Swept" "Air Blown" or "Washed" and if needed to be washed we need proof of the washout ticket. 

My question is it was brought to my attention that some of the truck drivers are also the feeds end destination and if they do not care what was in the trailer previously or do not feel it is necessary to take the time to clean it out they do not want to have to do so since they are the end customer. Has anyone else experienced this and how did you handle it? Was it like what happens if you take your car to the mechanic, they tell you something else needs repaired but you want to drive it home without the repair? You would have to sign off that you have been told about the problem and that you have chosen to not remedy it and are assuming all of the risk?

Just wondering if anyone else has experienced this? 

Sounds a bit more legal than I have experience in.