Sometimes is can be related to the diet. Some foods can just produce a different smell to the rabbit and the waste produced. The owner might not notice this as much as they are around it all the time, but a new owner of the rabbit an notice it as it is different from what they are used to. Changing the feed can help this, but it can take some time for you to notice a difference.
With spray and urine, the smell can also be diet related. As urine an be different colours, this is usually caused by the diet. Some foods could mean smellier urine and therefore smellier spray. A good litter can help with the smell, but this really only works if they are litter trained or you use litter in the whole cage.
Intact rabbits can smell more than spayed or neutered ones. It can be a bit more musky, especially with males.
Since breeders do keep many rabbits in a smaller space (like a barn or shed), any smells can be more just due to the numbers.
Try cleaning the scent glands and changing the pellets (remember to do it slowly though). You can also try wiping the rabbit down with a damp cloth to try to get rid of some body smells. Keep the cage clean and the area well ventilated. Hopefully the smell will go away in a little while.
