I've been on Amazon's "get free stuff" list for a few years. I review stuff honestly.

If the product is trash, I review it as such.

If it's good, it gets some notes about the good stuff and the parts that make it less-than-great.

If it's great (and I'm rather particular so most things fall short of "great"), then it's still gone over in detail.

If my opinion changes over time, either positively or negatively, then: I update the review.

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This is in-keeping with the program's terms of service, and nothing about those terms compels me to behave other-than-honestly. I'm not expecting to get kicked out of it anytime soon regardless of how many 1-star reviews I post.