I love it when I hear: 'the store screwed up' and 'those people are idiots'. READ THE LABELS!!! Buyer beware! Geez! Before you start slapping paint on something, invest a little time in reading up on it.
#1: ALWAYS USE A PRIMER. Use the RIGHT primer. If in doubt of the surface you are covering, rough up (sand) the surface, then prime with a shellac primer (Zinnser makes a good one). Most projects: oil 1 hour drying primer works well. Bare plaster or drywall: PVC primer.
#2: If you want OIL enamel: READ the cleanup section. If it says soap and water, voila! You have a water based product. If it is solvent based, it will tell you what type of solvent to cleanup with.
#3: What is the temperature, humidity, etc. of the room you are painting in? This is CRITICAL - I heard someone complain that the paint would not dry; come to find out, they were painting in temps below what the manufacturer recommended and applied an extra coat prior to getting the 1st cured.
While Home Depot may be guilty of hiring kids with little or no knowledge of paint chemistry, you, as the buyer and DYI painter are ultimately RESPONSIBLE for any and all errors made with the paint. If someone recommended that you put deisel fuel in your gas burning car, would you do it? The point is: you don't have to follow the kid's advice; the info you need is written (very small) on the label.