From the outset you as the founder have to be doing the sales, or then find yourself a co-founder (which is not the same as a SaaS sales rep) to help you out on the business side of things. But unless you do the sales, you will never figure out what will work, which part of the value prop is resonating and therefore you will never find product/market fit. Hiring a sales rep too early (prior to you getting a few customers on your own), will simply result in their inability to sell your product which you will attribute to their failure as a sales rep when in fact the product's value proposition isn't yet clear enough for any customers to buy at scale. So close the first accounts first on your own or get a co-founder on board who can, but don't go out and hire a SaaS sales rep until you know what the product really should be. Once you do know, you can easily hire a few SaaS sales reps on low retainer + hefty commission.