My understanding is that even if police were running that site it would still be fine, unless the site is actively reaching out to people encouraging them.
Standing on the corner selling drugs to people who ask: ok
Standing on the corner, asking people "hey, wanna buy some weed": borderline but probably still not entrapment
Standing on the corner, asking people "hey, wanna buy some weed", then pestering those who say "no thanks": Entrapment.
An undercover agent becoming a friend with someone, then pressuring them to buy weed for him even though that person really doesn't want to: very clearly entrapment.
Standing on the corner selling drugs to people who ask: ok
Standing on the corner, asking people "hey, wanna buy some weed": borderline but probably still not entrapment
Standing on the corner, asking people "hey, wanna buy some weed", then pestering those who say "no thanks": Entrapment.
An undercover agent becoming a friend with someone, then pressuring them to buy weed for him even though that person really doesn't want to: very clearly entrapment.