Memorial Day weekend "is when the stores have their big sales -- so it's very specific," says Mendelsohn, author of "thepurplebook."
What you might not know: If you want a wide selection and sale prices, find out if the store has pre-sale shopping, she says.
Here's how to take advantage: You go into the store before the sale -- pay for the item you want at the sale price, and pick it up or arrange to have it delivered during or after the sale, Mendelsohn says.
At Memorial Day sales, you can save up to 30%, which is significant on a big-ticket item. "A lot of times, they'll throw in free delivery," she says.