How to prepare the sales team to handle any negative feedback or issues that may arise post-launch?

I think its fair to assume that initial product feedback may sometimes be mixed. so It is important to capture as much of it as early as possible. At Amplitude we use a variety of different channels to begin with

-We have product feedback submissions that can be submitted on behalf of the customer by sales or customer success which we track in our PD operations via product board
-We have internal channels dedicated to product pillars consisting of a Swarm of experts PD+Design+Eng that can triage any issues raised by sales or success teams
-Finally we also have community monitoring across forums where we track any feedback and can respond acordingly

Sales teams like any other teams are armed and well enabled on what the product is capable of and not capable of ( limitations ) early on in the product life cycle, so its important to get this right in the messaging so it can be clearly communicated to customers early in the product launch