Good advice, higher end cameras are good for 100-200000 pix, but in each case its a return to a service centre for a new shutter (expensive!!!!!!) All good 2nd hand retailers will tell you how many pix a shutter has taken.
If a camera looks 'tired', scuffed or dented leave it alone. Most dealers have a regular clientele of customers who trade cameras regularly. They know who looks after them and who doesn't. Best buys are recent trade ups by regular amateurs. Pro cameras usually have a lot of surface wear as well as high shutter use. Its better to pay a bit more for a clean one, even if you have to extend the budget.