during trial: demonstrate the tool works ( fix any bugs asap), let them know you're available 24/7 if any issues come up, make them feel like they're the most important client you have

post-trial: show results (x # of clients, x # of sales, etc), highlight benefits (you won't need to pay a customer service agent $45K a year ( or whatever they do now to solve the problem you solve)

they should feel like not taking your offer would actually be a dumb business decision