With regards to yearly payment terms (or longer, we have some customers that pay for 2 years and 3 years in advance), check the TOS with the hosting company. Verify that they are a LEGIT business that has been in operation and have a following and reputation to back up quality services (this should be done with any host), but in the TOS check their cancellation process, or their termination process.
Sites being suspended or terminated for system abuse DOES happen - this is an event that any site that was configured to "X" users and then gets slammed with "Y" traffic is going to run into. We've seen many small websites start out and then expand into much larger operations - if the clients then had to upgrade. But then, we don't offer "UNLIMITED"
In the Terms of Service check the cancellation process and policy. Many hosts offer a prorated refund on cancellations. So if you sign up for 1 year, get the discount, and then choose to cancel after 6 months, they would revert the rate back to the regular rate and refund the balance.
Termination of service for CPU or Memory resources are often handled the same way. Again, it depends on the host, but almost every host treats a spammer differently and opt NOT to refund money if they abuse the system.
There's a lot to be said for the long term signup - it builds a loyalty and with smaller hosts you can build a great rapport with them. Of course, a host makes more money if you pay monthly
I've been the big fish in the small bowl with data centers before, and I've also been the little guy starting out, both paying on a monthly, quarterly, semi-annual or annual basis can be beneficial depending on what you're doing.
Take my gym membership - I'm pretty much committed for the year, so by paying a year in advance (up front) they knocked 20% off the price. Do I believe I'm getting value for my money - sure do! Do I foresee them closing down - not really, they're pretty reputable and have been in business for many years as a national chain. Do I foresee being asked to leave their facility for abuse of resources (equipment, staff etc etc) - not a chance. So prepaying for 1 year and getting the discount is to both my advantage and the clubs.
Hosting companies, are very similar - at least the ones I'm involved with are like that!