 re: How do I tell if a shirt has been screen printed or poly.. transfer?
Well, for starters if it's anything other than polyester it's not dye sublimation.
Dye sublimation tends to have somewhat subdued colours. Depending on what kind of printer was used you might see the signs of poor printing associated with inkjet printers (banding, poor colour fidelity, etc.). The black is often kind of faded looking, rather than a nice dark true black. If you pull the fabric apart the dye sublimation print will stretch very well - the picture will distort with the fabric, but there'll be absolutely no cracking, and you can see the dye is right in there.
The best thing to do would be to get something you know is dye sublimated and something you know is screenprinted side by side, and you should get a good feel for how to tell them apart.
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