Does virus testing really identify viruses

[nhman]

OK, so heres the story:
Just bought a wonderful and expensive orchid (Eria gigantea 'Waterfield') from a grower that I've had excellent luck with previously. ( I have probably over 25 orchids from this grower) I always virus test ANY orchid before letting it loose into my collection, using Agdia testing strips. This one plant tested positive for a virus on three separate tests.
So, I called the company.
I was told- appropriately - to send the plant back for a full refund, but then he stated that there were NO virus tests, no lab tests that "worked". Period!!
I find that this is difficult for my scientifically trained brain to accept. Why wouldn't they "work" at IDing a virus?
It IS rare that I get a positive test, I should note. I also don't smoke and wash my hands with an alcohol based prep between plants (tobacco smoke has been felt to be a possible disease vector to orchids and so has poor plant biosecurity)
Anyone have any thoughts to support that this concept is true (virus testing doesn't work), if not, I will continue to test any and all plants that cross my doorstep for virus.
I'm interested in what the experience and thoughts of this Board may be. Thanks in advance.