GET. IT. IN. WRITING!
When you get a job offer, no matter how much you like and trust the hiring manager, you must GET THE OFFER IN WRITING!
This is not negotiable.
If you accept an offer via handshake agreement, you WILL lose out at some point.
If no written offer has been provided, a good way to create an audit trail is to email the hiring manager and detail your understanding of the offer. CC yourself or locate that sent message then move that email to your do-not-delete folder.
If a company absolutely will NOT commit your offer to writing then whatever you’ve been promised is just smoke and mirrors, and you should RUN—not walk—to the nearest exit.
BEWARE the company that extends you a cheap offer for they will ALWAYS be cheap and will NEVER truly value you, nor your contribution.
Whatever the situation, don’t be wishy-washy and don’t drag things out. Just make your decision and don’t look back.
If you have to cut your hand off, far better to do it quickly with a sharp knife than to saw at it with a cafeteria spork.