Has anyone got any tips for negotiating with car salesmen as I always seem to get screwed over
Yep, buy toward the end of the month, as they'll bargain with you if they need to hit sales targets, which invariably they do.
Use the Parker's guide with them because it undervalues these cars, working in your favour.
Get a discount off the bat because of the erroneous service history.
Make out you've got another car you're considering seriously that costs slightly less and has something this one doesn't, e.g. 4 new tires and 12 months tax.
Don't answer your own questions when asking them stuff, to ensure they have to work to gain your interest, else you'll talk yourself into it without them doing much or showing they know much about the car. Some people ask questions then don't shut up and let the other person talk, out of nervousness.
Don't buy the first one you see! There are loads of VXs for sale.
Go on a few viewings of cars at garages to get in the swing of talking to salesmen, hearing the same old lines, looking at paperwork, service history, test driving.
Find a friendly local owner on this forum to drag along!