Nezzer, nothing wrong with knocking on cockpit doors, if you can get through the security. I for one don't mind at all chatting to guys/gals at the handlers/FBO's who are trying to get into the business and if they make a good impression I won't mind either giving them some pointers or even taking their CV if I know of someone who might be interested. We have a higher entry requirement, but that doesn't stop me handing a CV to someone if the guy/gal has impressed me.
Getting into charter sales is all well and good, but there are plenty of jets not on an AOC. If you are thinking about an entry level job, forget charter sales, that will only give you exposure to that company and go for a handling job at an airfield that handles multiple owners and operators, that would give you far greater exposure.