There is a lot of Betfair bots on the market today. I would separate all Betfair bots in few categories.
1. Trading Betfair bots. This kind of bots has many features for trading on Betfair, like greening up, stop loss, fill or kill, ladder interface, advanced graphs and other. Trading Betfair bots are usually semi-automated, this means that you have to be near your computer and make trading decisions while some features, like stop loss or fill or kill, are automated and require only a single click or defined conditions from you. These bots are usually used with Betfair trading strategies, especially in-play, when prices are highly volatile.
2. Read-only Betfair bots. They don’t place bets but read, analyse and collect Betfair information. These Betfair bots have different alerts and innovative market indicators. Other work like calculators helping you to follow a betting strategy, like dutching or some kind of staking plans. Such Betfair bots also offer betting history storing and graphs. They often come with betting systems and tipster services. Read-only Betfair bots which work like calculators, require you to place bets manually on Betfair or other betting exchange.
3. Fully automated Betfair bots. These betfair bots require one time setup, then they work in automated mode on your behalf. Selections can be predefined manually or chosen automatically from predefined formula or conditions. See Betsender for example of such Betfair bot. Often fully automated Betfair bots work with particular staking plan or betting system. Also some of them are designed to download selections from tipping services. I would say separately about server based Betfair bots or web bots. They run on their own private server and have web user interface which means you can access these bots from any computer which has internet connection and web browser. You just open specific web site where you setup the bot, then you can shut down your computer and the bot will still place your bets from it’s own server. One site which is designing server bots is Betgrail.
Also I would mention Betfair bots for mobiles as a separate group. It doesn’t have all features available in desktop bots, but can be handful if you are away from your computer. For Android you may check out this software: http://code.google.com/p/betonthemove/. For iPhone there is a good app as well: Mini Bet. Also Betfair has it’s own interface designed for iPhone users: https://iphone.betfair.com .
All Betfair bots use either Betfair API (free or commercial) or screen scraping. Free API is free of costs but limited to number of requests you can send to Betfair. Many Betfair bots use commercial API. It’s subscription based and vendor has to pay monthly subscription fee £200-£250 which is usually included into the final bot’s price. Commercial API allows virtually unlimited number of requests per second, but of course if you do too many requests according to Betfair terms you have to pay Transaction and Data Charges. Screen scraping is an HTTP technique, similar to that one which is used when you open Betfair in your browser. It’s free and allows the same request speed as commercial API, but it’s also a subject for Betfair transaction charges.
Remember that having a Betfair bot doesn’t guarantee that you win. Make sure you are familiar with the bot as much as you can before risking money. Read manuals, take your trial, ask questions before betting with the bot.