Your example of "sketchy" refers to inadequate or incomplete information about the walls. The term is used to describe something questionable about safety, truth or reliability. The walls are unsafe for some reason and therefore cannot be trusted for climbing. The term "sketchy" is commonly used to refer to questionable information or doubts concerning the truth about something. For example, information about an item for sale. "The car was on sale for a good price, but the owner's information about its history were "sketchy" at best." "The eyewitness claimed to have seen the crime, but her details about the location were a bit "sketchy."