Ian (above) hit the nail on the head. People give you some facts and 30% of the time they are wrong. I have been doing almost 900 inspections for the past 15 years. As a licensed builder and past industrial project manager I have seen many problems that if people could read into the future could be avoided. (Get the picture?) You will never know what you will run into no matter how many questions you ask.
My pricing structure is to divide homes into 3 age groups: 1995 to present; 1964 to 1994; and 1963 and older. The newer groups I charge slightly less the older groups have more issues, the middle group may or may not have aluminum wiring, lead paint, asbestos, etc.
Then I group all by square feet: up to 1,200; 1,201 to 1,700; 1,701 to 2,400; 2,401 to 3,100…and so on.
Then across the top I list 1-bath; 1.5 to 2.0 baths; 2.5 to 3.5 baths; 4.0 to 5.0 baths. This gets me into the ball park range.
Then finally I charge extra for 2’nd furnace, finished basements w/ wet bars or 2’nd kitchens there, 3 car and larger garages, crawl spaces take longer than same size unfinished basement; docks, seawalls; boat hoists, pole barns, radon testing, lead testing, mold testing, wells, septic tanks, etc.\
If the client is a first time home buyer pinching pennies and the home is vacant (not occupied) I may give a deduct. If home is smaller in size and does NOT have a garage and is occupied I always ask “how much stuff is there?” If sellers are HORDERS, it will take me a lot longer.
Finally, I always give a time frame…IE- it will take me 2 to 3 hours on sight. I hate to be rushed on larger older homes. Be honest.
Hope this helps.
BTW- In Michigan, this time of year, vacant homes that are winterized mess me up a lot. Many banks have the de-winterizing crews show up the same time you schedule the inspection and you wait (waste) an hour or so on them. Allow for that or get a promised time to start. or wear warm clothes.