I"ll add this: If Patrick HMD is going up and knocking on the door then he is trying to find someone at home. Also in several of the pictures I can clearly see that this place is right off a Farm to Market road. For all we know the owner buys and sells stuff and wouldn"t mind people stopping to look. Clearly the OP didn"t crawl over any fences or ignore any signs to go away. I don"t think he did anything wrong.
There"s several places in my area that are a lot like this one and the owners buy and sell stuff and I"ll stop by and the owner is not there. You don"t know they aren"t there until you get out and walk around looking for them. These guys make money by selling stuff and don"t bark at potential customers.