Startups are typically trying to find product / customer fit.
That drives salespeople nuts because they want to sell - not tweak product mix / pricing strategies. And they can be expensive if you don't have your product offering locked down.
Meanwhile, you expect sales to.. well, sell and not burn your capital reserves.
IF you are going to hire sales staff - make sure that 1) they understand the stage of customer development you are at and 2) you set realistic expectations about what they bring to the table.