What do I need to verify non-standard income for a lender?

[Slaiman Atayee]

I'm a salaried employee for my company and have a standard w-2 for the majority of my income but in the last year i've started doing things on the side like the occasional wholesale deal or some remodeling work, both of which I get via paid cash or wire. For a lender (and the underwriter), what do I need to "verify" those other non-standard sources of income? 

FYI - I have several properties already and have been through the standard mortgage/loan process several times with only my w-2 income in play so not looking for standard lending advice in that respect. I googled the subject above but can only find stuff related to standard income

Any help is appreciated!