Anyone that says "we will just do this temprarily" will get charged double and need to send that statement in writing with firm start and end dates along with the consequence of not meeting the deadline.
Once your average deal size hits >$250k touch nothing less than $100k if it's a new client, leave it to inside sales.
If someone (or a business) has ever paid you for anything they never get free work. Free product? Maybe, but never free work.
Put it in a contract, regardless if buying or selling, or it doesn't exist. When asked to modify something on the fly from that contract, "we'll let you know" is the only acceptable answer until you review with your team.
"I don't know but will try to find out" is acceptable. "Yes if..." is preferred.
"No." Can help you live longer and healthier.