A professional inspection is an assessment by someone with qualifications and experience relevant to the stated subject. The scope still needs to be defined.
What this means at your property
A roof specialist, electrician and structural engineer may each examine the same property for different reasons. Calling a visit “professional” does not mean it includes every system or resolves every hidden condition.
What should be agreed before the visit?
Confirm the purpose, areas to be examined, methods, limitations and written deliverable. Ask what further specialist work might be needed and whether the report distinguishes observations from conclusions about cause.