An advertiser can choose to pay per conversion instead of per click, but whether to send the conversion ping is always up to the advertiser. They don’t need to use something like Smile to get an excuse for not sending the ping: they can just not send the ping.
(Why send pings at all? The reason to pay per conversion is to let Google optimize for sending you the cheapest traffic that converts. Your bids still end up in auctions against others, though, and if Google’s estimate of how likely this traffic is to convert on your site is lower, the bids they’ll put in on your behalf are lower, and you’ll lose lots of auctions you’d have preferred to win.)
An advertiser can choose to pay per conversion instead of per click, but whether to send the conversion ping is always up to the advertiser. They don’t need to use something like Smile to get an excuse for not sending the ping: they can just not send the ping.
(Why send pings at all? The reason to pay per conversion is to let Google optimize for sending you the cheapest traffic that converts. Your bids still end up in auctions against others, though, and if Google’s estimate of how likely this traffic is to convert on your site is lower, the bids they’ll put in on your behalf are lower, and you’ll lose lots of auctions you’d have preferred to win.)