I'm an engineer/CEO/Founder of an unfunded startup (well, I guess you could say I'm the one providing the funding). So far I've been the only person who has done any work with this company. I don't have the business registered, I don't even have a separate bank account for the site's expenses. My business plan is to get lots of signups, and then sell advertising on the site, as the user-base is very focused.
I'm thinking of hiring a sales guy, whose job is to get in touch with companies and try to get them to purchase ad space on my site. Since right now the site does not make any profit, I don't have any money to pay such a person. But I understand some sales people work only by commission. How does this work? Will I only be able to get crappy sales guys to work under these conditions? Am I going to need to get funding first so I have money to pay the sales guy a salary?
Also, since I don't have any kind of financial/business infrastructure in place (bank accounts, tax forms, employment contracts), will that stuff impede me?
I saw from the comments that you already use Adwords, but really I would question changing from that.
You are much better spending your time and effort improving the site and getting more users than dealing with recruiting right now. You are kidding yourself if you think you can spend 3 days, find someone, sit back and wait for the money to roll in.
Chances are, you will go through many sales guys trying to find a good one. Each will take you a lot of time to find, and also to "induct". You will waste a lot of time here.
Even if you do find a great one, you will spend plenty of time managing/monitoring them.
I would focus on your product, and let adwords bring in some revenue while you build your userbase. When you are leaving plenty of money on the table with adwords, that's when you should look to do your own ad platform.
Have you tried to contact ad companies instead of finding the final customer yourself?
That way you could rent your space and they could show (maybe even manage) the ads themselves.