I have never hired sales people at startup but have had to convince other top quality people (including a senior Trip Advisor developer) to join. Here's my advice:
1) It is best if the founders get out and do the initial selling
2) If you do have to hire a sales person at the startup stage, DO NOT settle until you find a skilled one who is also genuinely passionate about your business....this is hard but worth it.
3) Offer them serious upside via big commissions and/or equity.