I had my lawyer draft a standard single page purchase agreement when I purchased my AC. It provided clarity toward who was selling, who was purchasing, agreed price, AC details, clear title free of liens, encumbrances, liabilities, claims; AC condition and inspections undertaken prior to purchase, additional items, spares, log books, ancillary equipment etc, dates, signatures.
The AC was due for its Annual so I had it flown to a LAME of my choice and offered to pay for the annual regardless of my final decision to purchase or not. Drove down to where the AC was, and went for a fly with owner after going over LAME's report. Got flown back down three weeks later after funds had cleared and conditions were good; filled up the tank, took off, circled overhead once for clear offs, flew home.
If somebody requests an inspection, if they are serious, it would be fair to expect them to offer to also pay for it. If they kick up a stink and expect you to pay for it then its probably not the right AC for them.