You begin having a garage sale twice a summer and continue doing so for several years, and you have a sort of "clientele"; you know the types of items that they like to purchase and set aside specific things for them. According to the UCC, you are a merchant.

True.

The UCC defines merchant as someone who deals in goods of the kind or otherwise by his occupation holds himself out as having knowledge or skill peculiar to the practices or goods involved in the transaction.

So, because you have developed a regular client base and knowledge of what customers want you have become a merchant under the UCC.