Step 1: Check out Sailingdog's "Inspection Trip Tips" That will give you a good grounding on what to look for and how to look for it when you are out kicking tires and checking out boats. This info will cut down on the likelihood of having surveys done on boats that you shouldn't have even gotten that involved in anyway.
Step 2: If it is a candidate to become YOUR boat, get YOUR surveyor to do YOUR survey.
First, your insurance company will likely want one, even if a survey was done a year ago. So you're gonna have to spend the money anyway.
Second, YOUR surveyor has YOUR interests at heart. Who knows who was invested in the previous surveys, or the quality of those surveys.
Third, an insurance survey is often a cursory survey, providing a basic overview of the boat's condition at the time of survey, while a purchase survey is more involved.
Fourth, a survey is a snapshot of the condition of a boat at a particular moment in time. A survey done two years ago, last year, even three months ago can have little value, especially if the boat has been in use since the survey was done. Who can say that the engine hasn't been overheated and the head warped, the jib sail shredded and stuffed back in the bag, and the keel bounced off a reef since the last survey was written up?
Fifth, a good survey won't cost you a dime. A survey on a boat up to 25 feet might cost you $3-400, possibly less. If that survey doesn't give you $4-500 worth of bargaining power, because of defects discovered yet undisclosed by the seller, than that is a boat that will give you at least $500 worth of peace of mind, because it must be a pretty good boat, and it has saved you from spending gas and time looking at more boats.