For the snakes ... it started as a way to get into CC's life. And then it shifted along the way because he genuinely enjoyed the snakes. And then it changed again after he realized that CC's father took the snakes as a way to control CC, which meant he couldn't break up with Yue Yue yet.
Both CC and his frenemy ChengYu realized that the people CC's father has watching over the snakes are trying to make a little money on the side by selling off the snakes ... that is how CC got one of the babies back a couple episodes ago. CC and CY had both decided independently to buy back and/or exchange new snakes for CC's originals. CC to get out from underneath his father, and CY to have something over CC. This part at the end of this episode is WSW coming up with the same plan as the other 2 .... but they all think they are the only ones doing it.
By buy back or exchange .... the snake in the pet store was one of CC's that the dad's handlers gave the shop owner to sell. There is more to the plan that hasn't been revealed yet, so I won't spoil that.