The older boats have wood in the stringers, transom, bulkheads, and sometimes cored with plywood (bulkheads, consoles, decks etc). The hulls are solid glass and are easy enough to repair. My 1976 Eastporter had rotten wooden gunnels and trim too. I would say if the boat is older (not composite materials) and contains wood (not recently rebuilt) it will need to be checked for moisture in the wood. Most surveyors tap with a small hammer and listen for a solid sound, and use moisture meters to detect water intrusion. Drilling into wet wood (transom or stringers) is an easy way to detect water intrusion if you are allowed to drill small holes (fill with thickened epoxy). If you get the boat for a steal consider it a project boat and rebuild it. If you are spending a good deal of money on a boat I would recommend a competent marine surveyor to get it inspected. I saw a beautiful almost new Seaway 21' that is being sold from a salvage company in Mendon, MA because the former owner hit a rock or shoal. It looks like a new boat but needs a few small patches of fiberglass (bottom of the hull). I believe it is around $20k with the motor that has very low hours (bottom of skeg looks like it got hit too). My old transom was like mulch due to water intrusion over 30 years- the original builder did not fiberglass the top of the transom properly. The Easterns and Seaways are good boats but many old ones will need to be rebuilt.