Dendrobiums yellow and black leaf spotting

[Kateo]

Hello! I am new to this group and l am seeking some advice. I have been successfully growing phals in the house for years. I decided to branch out to dendrobiums. I ordered my first 10 plant collection. It arrived today with different types of spots on the leaves. The seller said "these were sprayed by the original grower and will not affect plant".

I do NOT want to infect my orchid collection.

Can you help identify the problem and whether or not these are worth saving. Should I trust the seller or throw them away? Any other advise is welcome. The pics show three different types of spots on several plants.

Thanks!