Typically you would adjust revenue and the related cost of sales / opex to be on a gaap/accrual basis and underwrite based on the resulting adjusted ebitda. In a growing business, this typically results in a negative ebitda adjustment. Don't forget to look at both book ends (prior year end and current year end) as there will be revenues/costs reported in current year that are related to prior year. A QofE professional can help quantify these adjustments.

I may be misunderstanding the question but I'd venture to say it depends on the industry and the nature of the cash.

E.g. a heavy equipment vendor with a lot of International sales will see a great deal of cash coming in as escrow wires. I wouldn't discount that at all, (at least not for being cash anyway).

Conversely, if we're looking at till numbers for a bar or restaurant then yeah, I'd say some discounting would be justified.