But one day I was talking to the guy in the paint shop and he said to spray a layer on a scrap piece before each coat and use your finger to test if it's ready for another.
Did it say anthing like this in the product data sheet? If not, you may have gotten some bad advice.

Make sure the paint to reducer ratio is exactly what the data sheet says, and that it matches the temp conditions. Make sure your gun is set up correctly, with the right pressure, air and fluid adjustments. Make sure you're not laying down the paint too thick.

. . . . and practice on something you don't care about.