Pretty much every business in life has a middleman (or woman), and the best ones are those who provide a valuable service for each side with expertise or resources that neither would be able to bring to the table. Being an auction middleman (or woman; we'll start using the term "middleperson" here!) can be a lot of work as far as organization and coordination goes, but you can get commission out of it and end up with a lucrative side business.
Seek out sellers who can't make it to the auction house for whatever reason. Maybe they are elderly and don't wish to travel; maybe they live too far away for the trip to be worth it; or maybe they just don't want to go. Seek out these people with an advertisement in a place they would be likely to see it -- the auction house may even be willing to let you post something, either in their building or on their website. State your business: you are willing to market and sell their items at auction for a portion of the price.
Learn the product inside and out. Unless you're intimately familiar with the details of their merchandise, you likely won't be able to convince others to buy it. Know all of the little things: the exact name of the color of that vase, the harmless reason for that funny sound in the car's engine, the date the painting was purchased from the original artist.
Once you know all of this information, write up a convincing entry for the auction house's catalog, so potential customers can read about it. Put your persuasive writing to good use here! You may also have to pitch the item to the auctioneer, depending on how the particular auction house works; whether or not you have to convince the auctioneer to hawk it off, you'll need to give them enough information that they can turn around and explain it to the bidders.
When the items sell, collect your money! You'll want a percentage that makes your travel distance, your time spent at the auction house, and your effort all worth it, so be sure you aren't selling yourself short as far as how much commission you require. You'll probably have to collect the money and take it back to the original owner before you can take your percentage, since the owner will want to know how much they actually sold it for.
A garage sale is like a one-time business, so you want to be as savvy with your marketing choices as possible! GarageSaleCow.com is a place for free sale advertisements to be posted; visit us today