I automated the arbitrage via some python scripts to scrape the sites and a EJBs to run the logic years ago (I have degrees in Mathematics, Computational Statistics and Artificial Intelligence). And yes, I said "EJB"s. Site changes can futz me up for a while, but I get it back pretty quickly. I have to be careful to not bet too fast 'n hard, only placing a few a day otherwise I'll appear like a bot (it's still me doing it, the engine just takes the donkey work out; it lists possible bet combinations and I can still dig in if I want with the engine yanking back any hedging bets from the recent scrapes).
EULAs/Contracts? Most are just permutations on a theme, so it's pretty easy to have sets of "rules" that get loaded on a per-site/account basis and factored in (all done engine).
Been running this since mid-2008. Won about £315k less costs (kit, connection, tax) so that's about £200k. Not bad for 2 and a bit years. And I still have the day job. I could reduce the tax liability, but I really can't be bothered. This is (almost) free money to me anyway.
I run a "fantasy bet" system letting it select the top 5 on a daily basis to see how it would run fully-automated. It's pretty good, but the heuristics are not yet up to matching a skilled human. When it is, I plan to run it for a few years, make enough to retire (I won't need much) and then open source everything. It's all built on F/OSS and this is my way of giving back.
There's only one problem with the system I'm using....I'm a dirty great liar too!