Hi, thanks for your question.
I work at a main dealer, and whilst I'm not going to disclose which brand, it's toward the higher end of the market.
Selling ten to twelve cars per month, assuming you hit any other KPI's, will provide a good income in a higher end dealer. In a volume franchise that figure would doubtless be higher.
Discount levels vary enormously, so it's difficult to give an average figure, but there are plenty of reasonably accurate guides to the market for a particular car on various websites, and some of the online forums might be useful for you as well.
The level of discount will firstly be determined by the car you're trying to buy. If it's a fairly mainstream model there'll be less variation than on more niche models, but most dealers are prepared to be flexible on the right car. There are models where discounts would be minuscule, others where you can realistically get a deal which would be closer to a wholesale figure than a retail one!
Hints and tips?
Do your research. For example, know roughly what your PX is worth in the trade, know what rate your bank can lend money at, that kind of thing. It's so much easier for the consumer now than when I started selling cars!
I'd suggest if you're committed in your mind to buy at the right price to signal that early on in proceedings, and work with the sales executive. We only have limited discretion, and I've worked in regimes where even the traditional 'full tank of fuel' last ditch clincher had to have managerial sanction!
Approach the process with three potential outcomes in mind - your ideal price, the price you'd be prepared to take and an exit strategy. I'd also suggest being prepared to take a part exchange out of the equation as well - unless it's a model the dealer will retail a px is a bit of a hindrance to you and them, and it muddies the water. There are now many relatively stress free ways if selling cars into the trade if an ad on gumtree isn't your style!
Above all, timing and flexibility are key. Being prepared to compromise on colour and specification, to buy a physical stock car and to take delivery before the end of the month, or the quarter will bring by far the best deal for you, whether it's a new car you'd like or a used one.
HTH