A negative or even lukewarm reference can knock a candidate right out of contention for a job. The safest way to avoid having your search sabotaged by an unexpected bad reference is to carefully pre-screen your references.
Lay out your case in advance to potential reference givers and ask if they are in a position to support your candidacy by providing a positive recommendation. It is critical to give them an out so that they don't feel obligated to provide a reference, and perhaps provide a less than fully laudatory recommendation when contacted by a prospective employer. It can be best to make your request by email so that they can consider it objectively without the pressure of a face to face interaction.
Get the Reference in Writing
If you ask a potential reference to put a general recommendation in writing in advance, you will have a better idea regarding the tone and focus of their recommendation. The incorporation of recommendations into LinkedIn provides an opportunity to test drive potential reference writers. Try writing a few recommendations for LinkedIn contacts and then ask your connections to reciprocate on your behalf.
When You Are Worried About a Negative Reference
If you are worried that a previous manager (who you haven't listed as a reference) might provide a negative reference if contacted by an employer, the best strategy can be to provide as many other positive recommendations as possible to counteract the impact, or perhaps make it unnecessary for employers to seek input from that manager. In some cases, you might have a better relationship with your prior manager's boss and can enlist their support. In other situations, you can tap a combination of colleagues at your level, customers, and staff who reported to you in order to fill out your roster of references.
Check Your Own References
Some candidates will have a trusted friend, posing as a reference checker or a background checking service, reach out to a possibly troublesome previous supervisor to ascertain how they might respond to a check. Others hire a reference checking service to discover what past employers are saying about them.
Candidates who discover a potentially damaging reference might then initiate dialogue with the manger in an attempt to negotiate a more positive recommendation. If that effort is unsuccessful, you could consider contacting the Human Resources (HR) department of your former employer to mention that your search is being adversely impacted by a former manager's negative recommendation. In some cases, HR will advise the manager to avoid such references as a matter of policy to avoid legal liability or negative publicity.
Negotiating a Good Reference
If you leave an employer under difficult circumstances, it is sometimes possible to negotiate a positive recommendation as part of the severance process.
Of course, the best way to avoid negative recommendations is to cultivate positive relationships with managers, whenever possible, and to resist the temptation of saying anything negative when leaving a job.