Many agents and editors request sample pages with authors' submissions. They want your novel to hook them on the very first page. If it doesn't interest them, they won't want to read further. That makes them less likely to request more. For $5, I'll critique the first 250 words of your fiction novel. In the critique, I'll tell you what works and what doesn't. Does your character make me want to care? Does it start in the "right" place? Can it hold my interest and make me want to read more? Does it flow? You'll want all of these questions answered before you hit "send" on your query.
You also have the option of choosing the first three chapters/20,000 words, or full manuscript to be critiqued.