Verbal phrase "savoir gré" (to be grateful) means knowing that one is satisfied or dissatisfied with something or someone. It is a very sustained expression.
Je lui en sais gré
Je vous saurais gré de me faire parvenir le colis.
Il ne sait aucun gré de ce qu'on a fait pour lui.
The main difficulty of this expression comes from the oral confusion with the verb "être". "je vous serais gré" instead of "je vous saurais gré".
A simple way to stop making this mistake is to say that when you owe something to someone, you "know" it and so you "are grateful" (sait gré).