Is their sales terminology misleading?
"We promise 99% website uptime?" That sounds pretty good, right? Yet that one percent allows your host to be down 432 minutes or 7.2 hours every month and still stay within their contractual terms. And of course since you aren't monitoring your website every minute of every day, chances are that they could be down 10 times that amount and you'd never be able to account for all the downtime.
Email newsletter providers often state a 99% email delivery rate, even though most newsletters fall victim to at least 25% of the list being undeliverable due to changing email addresses and being kicked out with spam filters. Smaller hosts that don't keep up with the latest technology are often less efficient than that. So what's up with that 99% thing?
In most cases, they are redefining delivery rate as that rate after those bounces occur.
Search Engine Guarantees
Search engine optimization companies often guarantee you a certain ranking on a number of terms. However, what they fail to tell you is that first, they cannot guarantee anything on a search engine they don't own, and second, you don't get to pick the term. Imagine any company actually promising that a small insurance agent in Dubuque Iowa would compete on Google page one for "insurance" and beat Allstate, State Farm, Prudential, Geico, Progressive, Nationwide, and about 100 other such similar companies. It's not going to happen.
The fact is that no search engine is actually obligated to you to provide you with a listing at all. Obviously, no SEO company can provide you with a guarantee for such services.
When you hear the word guarantee, listen closely, ask questions, but mostly, get ready to run.