If you are on a quiet street, then people should see that there is a sale on both sides, and walk across. You mention it as a highway. I would only stop at a sale that was on my side of the highway usually, and not very likely walk across a highway to go to one on the other side. So I think that part depends on what the road itself is like.
I think that if things were put out more along the front yard instead of along the sidewalk, then people could see what was there better. And if you are sitting out there and wave, they are more apt to stop. I often don't stop unless I see people out in the yard.
I also like to negotiate prices, so if I make an offer on some items that I think are priced too high, and they will not even consider reducing the price; soon I decide that everything else is probably too high also, and just leave.
When I am having a sale, I usually start at the best price I hope to get, and then if people are not interested, I start lowering prices until they get down to where people do start buying things, and take any offers that seem reasonable.