trading in fish with LFS -- did I cause Ick somehow?

[StephenP2003]

A couple weeks ago, I brought 30 platys to my LFS. Today, I messaged my LFS and asked if they wanted some guppies. They said, "Sure, we can take some guppies.  What are your water parameters though?  Your platys all came down with really nasty ick last time you brought us some."

I told them my parameters (75 degrees, 10-12 dGH, 8 ph, 10-20 ppm nitrates, same as the platys), and they said, "Pretty similar to what we keep our guppies at so we'd be able to take some in."

So I'm just curious, what could I have done personally that made these fish get ick in their store? I haven't had to deal with an ick outbreak since last year, and this LFS pretty commonly has about a third of their tanks with a "not for sale" sign because the fish are being treated with something, and they've told me more than once that they lost an entire stock in a display tank due to ick -- so it's my gut reaction to sort of scoff at the notion that somehow this is my fault. But, I wanted to ask anyway in case there's something I'm not considering. 

[Cory]

It sounds like your fish probably got sick there from what they have going on. There is a chance you can bring it, but if you fish didn't come down with it, it's unlikely. 

[StephenP2003]

3 hours ago, Cory said:

It sounds like your fish probably got sick there from what they have going on. There is a chance you can bring it, but if you fish didn't come down with it, it's unlikely. 

Thanks for the reply. No ick outbreak for me since last year, and thanks to my eagle-eyed wife, I was able to start treatment early every time, and never lost a fish from it. 

[FrostiesFishes]

More often then not it’s something the store has going on.