I get a TON of deal emails every day. I get several from Groupon each day, for example. (I didn’t even sign up specifically to get all of them but I don’t really mind them as they go into a folder that doesn’t ding my phone every time I get one.) The number one way these deal sites can make sure I do NOT buy something that I might have otherwise is to disclude the actual deal from the subject line. I skim through emails without opening them and then “mark as read” the ones not worth opening in one swoop. An email from Shutterfly saying “8×8 Hardcover Photobook for $8″ is FAR more effective than a competing company’s email of “Rake in the savings this fall.” I didn’t even open the second email.
Most of us know a deal when we see it because it will be something we are used to buying regularly. The critical part of that is “when we see it.”