Do your research, decide what you'd be happy paying and try to stick to it.
Make it obvious you're prepared to buy there and then if their price is right. Ask the dealer for their best price (it may be lower than you're expecting, so always get that first), tell them what you've been quoted elsewhere and see what they say (lie if you want but keep it realistic and quote a source, they're unlikely to check). If you get a price you like fine but if the dealer won't get there straight away, walk away and tell them you're not happy but will think about it and I'd put money on them ringing you in the next day or two and either matching what you asked for or at worse a much better offer).
The worse that can happen is you'll have to give in and accept what they've quoted but if you do make it conditional on having something thrown in, every Panda needs mats and a locking petrol cap so thats £40 quid sweeter straight away, you could also try for some free servicing.
You should be able to get closer to 9k for a new one, perhaps better depending on your will power.