There is an Inspection Contingency in most contracts and if yours doesn't have one then write one on an addendum that references back to the original contract something like this, "Addendum #1, dated xx/xx/xxx it is hereby made a part of and modifies the Purchase Contract dated xx/xx/xxxx for the purchase of the subject property known as "12345 ABC St., Any City, Any State, Any Zip" as follows;
First and foremost, I am not an attorney nor dispensing legal advice but simply making a suggestion as to one way to word this type of clause and every buyer should seek their own legal council to verify the exact wording best used for you and your situation and state laws. All that said, here is how I might word it here in California...
"Seller to allow buyer and his home inspector/contractors to conduct all inspections within X number of days from the date of acceptance of the original purchase agreement and/or all connected counter-offers. Buyer will give seller notice of at least 24 hours before access to home is needed and agrees to hold seller harmless for any damage caused by buyer and or his inspectors/contractors. Buyer might need access on more than one occasion due to potential scheduling conflicts of various inspectors/contractors."
With this wording it allows you to do your initial inspection with your contractor(s) then come back when you find a buyer to allow them to verify the condition of the subject property is suitable to that buyer's needs. Best of luck!
IMHO...