A pre-purchase inspection is not an annual inspection, although the buyer and seller could agree to such an arrangement. The object is to examine the aircraft for damage and wear that might not be evident to an untrained eye and to form an educated guess as to maintenance problems that might arise in the future.
Obviously, the outcome of a pre-purchase inspection is likely to affect price. If a mechanic discovers a serious problem, the buyer is not likely to close the deal without a reduction in price equal to the cost of the repair. For that reason, the seller may be wary of such an inspection. Nevertheless, it is to the buyer's advantage to insist upon one. The aircraft may be found to be unairworthy because of faulty equipment or lack of compliance with an airworthiness directive. Once the deal is closed and the buyer takes possession of the aircraft, it will be extremely difficult to force the previous owner to bear the cost of repairs that should have been performed before the sale.
The extent of a prepurchase inspection depends upon the complexity of the aircraft and the wishes of the buyer. The buyer should specify the shop conducting the inspection or annual, but it is often the seller who rules in this decision. If that is the case, the buyer is well advised to evaluate the shop's credibility and reputation.