How much under the asking price can you reasonably offer for a reasonably priced used car (I don't want to piss them off!)

[TomasinaTheTankEngine]

but I obviously want to get a good a deal as possible.
It's on for £14k.
I'm not trading in anything or needing finance.
They already give a years warranty.
Is £13k too low to start?
I'd like to get it for £13.5.
Any thoughts?

They’ll have worked out what they want for it and rounded up to the nearest thousand (if you think it’s reasonably priced). So their number will likely start with 13 anyway. Offering £13k seems sensible, definitely not cheeky.