There seem to be a lot of good quality chisels around secondhand, but the very least most of them need to put them back into good working order is a regrind of the primary bevel, back-flattening if you feel the duty the chisel will be used for requires it, and honing. Sometimes that can be a five minute job, sometimes rather longer.
Planes are more tricky. Even the good models of plane from pre-war era will require some fettling, even if it's just cleaning and sharpening. Buying almost sight unseen off Ebay can be hit and miss, buying at bootfairs is fine if you know what's what with planes. The best bet is probably buying from reputable dealers - you can get your money back if not happy, and the good dealers want to maintain their good name, so don't misrepresent what they're selling.
Almost anything that was good quality when it was made can be returned to good quality with a little knowledge and some effort. If it was tat in the first place, it'll always be tat however much effort is expended in fettling it. Stick to stuff that was quality to start with, and be prepared to pay a bit more for it once rather than buy something dirt cheap twice or three times.
