What is the difference between SEM or PPC and search arbitrage?
SEM and PPC describe an advertiser paying a search engine for clicks to sell its own product. Search arbitrage sits on the other side: a publisher is paid by the search engine when visitors click those advertisers' ads on its pages. One is buying search ads to make a sale; the other is hosting search ads to earn a share.
SEM and PPC are the advertiser's vocabulary: Maximum CPC bid, Quality Score, Ad Rank, keyword match type. The advertiser's goal is a customer.
A search arbitrageur uses the same auction from the opposite end. The advertiser's CPC, less the shares kept along the chain, becomes the publisher's RPC. Understanding the advertiser's side still helps an arbitrageur a great deal, because it explains why some keywords pay well and why prices move. The one place the two roles combine is Search-to-search, where an operator buys a search ad as an advertiser and monetises the visitor as a publisher.