There are four deceiving practices you need to know before you buy a bird’s nest from anybody else:
Gluing: Birds’ nests are built by swallows depositing strips of saliva to create a home for their offspring. The saliva is very rich in protein and the building process takes at least two and a half months. During that process, the bird feathers and other impurities can get mixed into the layers of the nest.  Therefore, each nest undergoes a painstakingly laborious cleaning process involving magnifying glasses and tweezers.  That cleaning process can leave holes in the nest which doesn’t affect the efficacy but lowers the commercial grade of the nest. However, some processors will create a paste from seaweed, fish bone powder, and other substances in order to cover the holes. Some go as far as smoothing out the crevices and adding as much as possible of the relatively cheap paste in order to double the weight of the processed nests. We have even seen bird’s nests that were covered with non-edible rubber. The non-edible rubber covers the bird's nest for a long time and can preserve the nest better, but it will permeate into the layers and will not wash off. In people with a weak digestive system, it causes gastrointestinal discomfort and can harm the function of the digestive system.