Water stains on bulkheads, partitions. Examination of raw wood behind interior structures will usually leave clear evidence of a boat that has sunk. Often times the water lines are clearly apparent. They are usually to be found in areas that are hard to reach. An older boat with too many new replacements.
Older boat is too clean and has virtually nothing personal on it.
When there are no signs of anyone having owned the boat, one has to wonder why. While it is not the surveyor's responsibility to research the past history of the vessel, he does need to do something to protect himself. Many times a survey will reveal suspicions of sinking or other serious damage that may be hard to prove. Making such an allegation without being able to prove it could cost the surveyor dearly. So could finding obscure evidence but not reporting it.