Sales can be a cut throat business to get into, especially commissioned based ones. I took on the philosophy of actually trying to help the customer find what THEY wanted and not the most expensive crap out there and it worked out well. The biggest tip that can help your sales game is product knowledge. If you can supply the customer with enough information to feel safe about making a purchase and you have that product it should be a done deal. They are there because they need something, its your job to help them find it.