Your current employer know you are looking for job before you ready to give notice.
When start to look for another job, many employers will see you as disloyal or short-timer. Then, they will start to give you some small assignment, reduce the budget of your current project and in some case maybe even fire you. If your boss finds out that you finding new job, the best solution for you is not to lie. Find the perfect opportunity to speak to your boss about the reason you find another job and not hiding from him. This will let your boss feel you are a responsible employee that you communicate well with your boss before you leave.
You know you won’t get good reference from your most recent manager
It maybe not enough if just not listing the boss or employer that give you negative review because the reference-checkers will call anyone that worked with you and ask them about you even if they are not on the list. The other way is to have luck on human resources manager that wiling to speak to your old boss on your behalf. If all these failed, then you might need to tell your new employer honestly about the relationship between you and your past employer and prepared for question from current potential employer.
A company told you an offer is coming so you stop your search but it never come
A company told you that they have make you an offer and ready the paperwork and agreement. However, it never come. When you trying to message them about the offer, they will just say they are working on it. Therefore, remember that you only get an offer when you receive a formal offer letter. Never stop your job search unless you receive formal offer letter from company and keep up the search until you find a job.
You accept job offer, resign your current job but the offer revoked.
This situation usually not common in the market because you have accept the offer that provided by your new employer. If this situation happens, you can try to ask for compensation from the parties that revoked the offer since you are jobless now and just resign from the job. Another way is to check with your old employer whether they willing to let you stay but the it will be an awful situation where employer will have bad image on you.