The industry is focused hard these days on the process of pre-qualification. This makes some sense with the tighter credit guidelines that now apply as a result of the mortgage meltdown a few years ago. Realtors generally want to have some assurance that potential buyers will be eligible to secure financing if needed. However, this preliminary process is just that - preliminary - and not a mortgage commitment.
In turn, the strength of the pre-qualification depends in large part upon the expertise of the mortgage consultant to conduct a thorough, up-front interview. The quality of this intake can vary greatly, so you are well advised to start the process smartly.
The pre-qualification involves the review of a variety of factors including income, employment, savings, debt, credit history, and potential property interests. It is a lot of information - some of which potentially feels personal and confidential. We become fast friends! Ideally though, you come away with a better sense of how the mortgage process works, what you can afford, and what mortgage debt to anticipate.
Remember - it's a general conversation that is not binding either on you or any lender. We may revisit this process several times along the way. And it should not substitute for your having a proper mortgage contingency provision in your eventual purchase contract.