Being almost pounced on by the closest salesperson the instant I walk onto a lot is a huge turn off for me. However, at some point, it's not bad practice for one to come out and let their presence known, at least to be the one to stake claim on my sale. A couple of hours - a little much if you ask me. Don't follow me around, but at least pop by so say that they noticed me and they're there if I need anything. If they're not interested in the sell, I'm not terribly interested in the buy unless there is a fantastic deal to be had.