yes, ebay ,can get alerts if the same pc is being used to bid on the same listing placed in the IP address
but not sure how enforced is, and it can always be done with computers across the country, let say , I tell my sister in Ca to bid up to 30 on my listing , then I'm sure that my item will sell for more than that, and if it doesn't sell to anyone else, I can just cancel her transactions , there is ways to get around it ,but if the same bidders are always on the same sellers listing , then it also will raise flags if they really want to enforce it I guess, Does ebay enforce it, I don't think so, the more people pay for an item, the more their fees are going to be