While I don't regret my level 3 survey or think it waste of money, you do need to know how to decipher one because the results can look worrying.
I can almost 100% guarantee it'll say there's high levels of moisture in the walls which indicate damp (penetrating or otherwise) and the timbers should be inspected for damp/rot as it's common in older properties.
My report said the downstairs floor joists should be inspected by a specialist......they're concrete floors. The house is also 130 years old, it was built with open fires and a level of draughtyness that would lead to a high level of natural ventilation. The previous owner had used modern paints on the interior of the walls causing a waterproof barrier, moisture was building up. I only understood his because I currently live in an almost identical house so know what to look for and what's "normal" for an older property.
Looking at the report again, the inspector couldn't lift the carpets to look so he had to comment on what he might have found to cover his backside. There were actually several comments where he stated he wasn't able to get access to or see certain things then said the worse case scenario of what might be there.
What were useful were the comments made on the roof, back patio and ceilings. He indicated issues that would need to be looked at at some point and helped me decide if the price and work was worth it. Funnily enough, the original part of the house had fewer issues than the much newer extension on the back :)