Yes, there is a good chance sending a manuscript to an agent or editor will get it rejected. Sometimes the manuscript isn't good enough, sometimes the person you're sending it to simply doesn't like it. Writing is a highly subjective business, but dealing with rejection is part of it.
If you do the legwork and look into people who sell the type of manuscript you have on offer, you can have representation for less than $90.
Agents and editors don't have submission guidelines for nothing. They won't look at some internet page, they expect emailed electrons or paper pages.