Welcome to TNet, keif. I'm looking for items to sell that are relatively easy to ship and that I can make a profit of at least $50. Personally, I don't find it worth my time to spend most of a Saturday going to dozens of yard sales hoping to find some items that meet those criteria. My experience has been that 90+ percent of yard sales have nothing of any interest to me.
When reviewing ads, I'm looking for pictures or descriptions that at least hint at having good potential for high value items like that. I generally dismiss yard sale ads that advertise mostly clothes and/or kid stuff or give no info (or very little info) about the type of items they have. I also pay attention to the neighborhood where the sale is located. I usually look for an attractive sale in a higher income area as these locations tend to have better quality stuff. Here is an example posted on Craigslist today that I have NO interest in:
Multi-family Yard Sale this Saturday (7/11) to include housewares, clothes, and baby/kid's clothes & toys!
This sale is also in an area with a lot of apartments and small "starter" houses for young families. The odds of finding anything of value at this sale are very small so I won't waste my time on it. I usually find only one or two sales each weekend that are worth going to.
I also avoid estate sales run by professional outfits. These are commonly known as "tag sales" as the company will put a price tag on everything. My experience has been that these companies ask full retail value for everything and I HATE the mob of people that invariably show up to these things. I have found a few good deals on the second day of such sales when they reduce the prices but that is rare.
Also, I don't limit myself to just yard sales. I also frequent auctions but I'm selective about these as well. Generally, the auction companies will post LOTS of photos of the items being sold so I need to see some indication there is valuable and interesting stuff. Online auctions tend to be expensive so I prefer on-site auctions. The down side is you can spend a lot of time waiting for the items you want to come up for sale. But I enjoy the auction atmosphere so I don't mind spending a few hours hanging around and watching the action.
It's really a question of what fits your personal style. All of the above is more guideline than rule and I do deviate from these on occasion. I hope that helps some. Best of luck to you. I hope to see you posting you cool finds soon!