You should use documents, when possible, as your primary source of verification. Examples could include paystubs, rent receipts, or utility bills. Although documentary evidence should be the primary source of evidence, you should not limit your search to a single document or source. For example, if you have a few check stubs were one is very different, don't just average it in. Speak with the client or the employer and try and get to the bottom of what happened that pay period. Don't go by the stub alone.
If information provided by a source that contradicts your client, you should always give the client an opportunity to resolve that discrepancy. Documentary evidence is evidence of just one point in a client's life. While you are sometimes able to anticipate using this period in life, this is not always the case.
When documentary evidence can't be obtained, you should use whatever alternate sources available – such as collateral contacts or home visits.