IN MY OPINION-
A yard sale is an ad hoc event, sometimes even defined in a City Municipal Code. It is a personal, or sometimes a small group of neighbours coming together, to sell their items- on their property.
A FLEA MAKET- is an organized venture, usually on an ongoing scheduled basis, where people sell their wares- on ANOTHER person's property.
I work by the following model- give me an item, and I will likely add it to my collection. Give me two or three similar items, and I will trade the additional one(s) for something I want. Give me access to LARGE QUANTITIES of similar items- and I can run a business.
I always have a problem trying to write copy for a SINGLE item- knowing that once it sold- there are no more. ENDLESS REPETITION, selling similar items makes life so much easier.
Sellers who come to eBay with a "YARD SALE" concept, often do not have the knowledge to accurately describe their wares. And, the dissimilarity in items offered is not likely to lead to the repeat business THAT MOST LARGE SELLERS HAVE.
On the other hand- as a buyer- I LOVE !!! the deals I get buying NOT AS DESCRIBED items- and from my experience, knowing exactly what they are! (items not accurately described- by omission, or lack of knowledge- often not at all deliberate) Knowledge is key, and as in any situation, it can well be used to your advantage. Everyday, items sell on eBay for a mere fraction of their real, or intrinsic, value. That is a reality. However, as a seller it makes little sense selling items for a fraction of their worth. And, in the long run, it is not a good model for a business.