You just have to be careful in your search, and plan ahead (no impulse buys unless you KNOW they're real and you're not going to find them elsewhere for that price).
Money may be a sore topic if you are an earth sign trying to rein in an air sign's impulse buys.
Make a shopping list and stick to it, avoiding impulse buys.
Make just one grocery shopping trip each month to avoid impulse buys.
This will help keep impulse buys in check.