For important items, specialist inspection may be worth more than ten extra photographs
If value depends heavily on details that are difficult to interpret, consider inspection by a technician, luthier or specialist competent in that category and period.
Define in advance what needs checking: authenticity, originality of specific components, safety, structural repairs or functional condition.
Specialist assessment does not replace transaction terms and does not guarantee future market value; it reduces technical uncertainty.
Keep the report, or at least a clear record of what was checked and any limitations.