Comment by megolodan

You're not wrong that its easy to get relatively obscure IP addresses cheaply, however youll be sharing them with lots of folks potentially damaging reputation.

At scale, say P2P-book becomes the largest social networking site, all bad actors will be focused on using it and they will likely be sharing IP's, comingiling their reputation.

Sharing account ID's across IP would also be penalized.

People who post consistently from the same IP / MAC would be boosted, those are real people.

Of course before one is the biggest game in town you will simply not be on the radar, so using a captcha as well will be useful to prevent bots.