If you are going to buy a vintage guitar, and if your purse permits what your soul craves, please do not run into the closest shop that claims to sell true vintages dating from the times of the Mesopotamian civilization. Wait a little, do your own research, go through guides, and only then run to the local shop. Believe me when I say that you need the knowledge before you actually go for the thing, unless you want to end up on the wrong side of the deal, considerably poorer and maybe a little wiser too.
The question is, do you really know your vintage? Would you really be able to spot the difference? Do you really follow the history of guitars so thoroughly as to be able to name the year of a particular stratocaster at a glance?
If you are relatively new to the arena of vintages, get accustomed first. Judge your purse, judge the make and the year, judge everything that you think you should judge, and then some.
Be aware of the possibility that the local seller you have in mind might not possess a vintage guitar at all. Vintages are not that easy to come across, for if they did then they would not be so valuable any more, would they? But there are lots of places from where you can get to know whether a vintage guitar that has been put up for sell. There are newspaper ads and there is the internet. Nowadays you can get to know about a vintage that is up for sale even if it is in the next state.
One thing that you must be careful of in case you are ordering the guitar over the net or from a distance, is never to pay the full amount in advance. Promises are made to be broken, and a vintage might turn out not to possess the advertised quality, when it actually arrives at your doorstep. Always go for a post-paid mailing service. Do not pay until the instrument actually arrives at your place. This is one way of ensuring a minimum quality even if it is not totally fool proof.
The best thing to do would be to go to the shop itself that sells the vintage. Go and try it for yourself. Also ask for appraisals of the instrument. There are professional agencies that appraise guitars as well as other instruments for a fee. And their certification is more or less dependable.
After you see the appraisal, do not buy immediately, if you can withstand the delay. Do some research for yourself and find out if the price the shop is asking for is fair. At times, a shop will charge a hugely inflated price. If it is a consignment shop, the actual owner would not even get to know the price at which the instrument changed hands.
And if you do not check out the facts and figures beforehand, you might be led onto paying a lot more than you actually should. Reselling agencies often deliberately overprice their stuff to create a 'snob appeal' or an impression of value which the instrument perhaps doesn't really deserve. So be prepared to haggle quite a bit, and do not pay more than what your research has suggested as a fair price.