Kinkade pieces were issued with certificates and, on much of the production, a hologram. Those confirm the piece came through the official publishing channel. They do not confer scarcity and they do not support the retail price.
The edition marking is what matters commercially. Editions ran to very large numbers, and there were multiple tiers — standard numbered editions, artist's proofs, and small premium tiers with hand highlighting by named studio artists or by Kinkade himself. Only the smallest tiers have any collector market at all.
Hand highlighting is a genuine practice: studio-trained artists applied paint highlights to canvas transfers, and the piece is described accordingly. Highlighting applied by Kinkade personally is a distinct and much smaller category.
The practical check is therefore not authenticity but tier: read the certificate and the markings to establish which edition and which highlighting level, then look up completed sales for that specific tier.