Okay, who else gets annoyed when a grocery or department store cashier hands you back your receipt and thanks you by name, even though you know they have no clue who you are? This is something retail clerks with the ability to see a customer's name during the transaction are taught to do to maintain "good customer service" -- yet there are very few people who actually enjoy it. (If you're one of those people, kudos! You make a cashier's work worth it.) But when it comes to helping out your customers, there are a few things you can take away from the retail industry, even if you don't thank every shopper by name.
Offering bags as a courtesy service is pretty much a given at a garage sale. Save up your plastic grocery bags for a month, or (if you're green and take groceries home in the reusable bags) ask around for some; most people have plenty to spare. A good rule of thumb is to offer a bag when your customer purchased more than three or four items, or when they purchased one big item and many small ones. Let them know you have bags available at no extra cost and are certainly happy to give them one.
Carry-out has long been a service offered by grocery stores, even to customers who clearly don't need it. If you have more than one person running your garage sale, you may consider offering to help carry a customer's items if they appear to be struggling, or if you have a good idea that they might run into some trouble on their way out. However, if you're short-handed and are flooded with shoppers, you may have to decline for the sake of your money's safety. Try, though, to arrange it so that you can help a customer to their car.
A customer is interested in buying your couch, but you saw them drive up in a two-door sports car. You didn't expect the next words out of their mouth: "Can you help me haul the item to my house? I just live a few blocks down that way..." Hauling items is in no way your responsibility. If you're selling big items, it's pretty likely that you didn't want to deal with dragging them anywhere in the first place. You certainly can offer to help out, but if you do, tell them they will have to wait until the sale is over to get their item. Generally, though, this seems counter-productive.
Sometimes, shoppers will ask you to hold items for them while they continue shopping, or until they can come back with the right change. Carefully consider this on an item-to-item basis. If it's clear that the customer is very enthusiastic about your particular item, you can consider setting it aside. However, some people shop garage sales like retail stores -- hunting down the best price and buying the item from whoever offers that price. You may find that you've held a perfectly sellable item for a shopper who never return. If it seems like they might not return, tell them you'll hold it for a few hours, or set a no-holds policy ahead of time.
What about that customer who wants his change in four ones, three quarters, two dimes, and five pennies? Are you obligated to make the change the customer requests? If you have the change and it won't put you out for future transactions -- yes, it's a courtesy thing. But if you're really strapped for quarters and absolutely can't afford to do it, just be up front about it. Let them know the reason you can't make the change they want; there's no need to be a jerk about it.
If you like what you've read here, why not do your customers another courtesy and point them to GarageSaleCow.com? They can list and find garage sales in the area for free, and participate in all the great resources the nation's largest garage sale website provides!