Q: Is it good enough if an endorser says “thank you” to the sponsoring company?
A: No. A “thank you” to a company or a brand doesn’t necessarily communicate that the endorser got something for free or that they were given something in exchange for an endorsement. The person posting in social media could just be thanking a company or brand for providing a great product or service. But “Thanks XYZ for the free product” or “Thanks XYZ for the gift of ABC product” would be good enough – if that’s all you got from XYZ. If that’s too long, there’s “Sponsored” or “Ad.”