Just to add to what @hawkice said already, you can offer them a money back period or offer a short free trial like for 7-10 days BUT take credit card upfront. Always take credit card upfront, period. If not, then you will get tons of tire kickers and time wasters. For bootstrapped, it will not be of too much use to you and may add unnecessary support time.
It is simple. I offer a 30 day money back guarantee. But if you cannot commit to credit card on day 1 knowing that you have nothing to lose, then you are not the customer I want.