Pests in plant shop

Last month I sadly killed a gorgeous Dieffenbachia I had for a few weeks by treating a whitefly infestation incorrectly. I was disappointed because it was growing so well.

Yesterday I passed the shop I bought it in and decided to go in and get another. I was looking through the plants and realised the leaves were covered in dead pests 😳 It was like the shop had treated them but not cleaned off the plant afterwards.

Now I think I might have actually bought an infested plant originally and I'm so annoyed, I know I messed up in the treatment but this shop has a really good reputation.