Interview Question-Help

I've come across conflicting information on the guides that I've looked at. For example, one question discussing the balance sheet after an acquisition: "If you've paid exactly what the Shareholder's Equity is worth -e.g., you paid $1000 in cash and the seller has $1000 in equity, then there are no problems. The combined cash balance decreases by $1000 and so will the combined equity. I understand that you need to create goodwill to balance out the purchase price you've paid but am becoming very confused about how the combined equity value would decrease in this example if there was no equity financing taking place. I obviously am missing something here so if someone could clarify this overall concept I'd be pretty appreciative. Thanks:)