They need to be honest because they are risking losing followers and about where they are going to get funds to maintain and make a profit from their reviews, there is such a thing as an affiliate, take the case of gambling reviews if the operators of these gambling review sites are honest, they are likely to get more active referrals from casinos, people first look on how honest the reviews are before joining, in the case of ICO or NFT they should still honesty and factual in their reviews and just put a disclaimer that they are putting honest reviews whether they pay to get a listing or not.