You should always interview prospective disc jockeys, just as you would any employee. Whatever you do, don't just hire someone sight unseen; you never know what you'll get. That may be fine for a box of chocolates, but not for your party, especially if it's corporate.
Ask all your prospective disc jockeys for references. If they're professionals, they shouldn't mind. After all, you're hiring them as an employee, however short-term the contract. If a DJ won't give you any references, move on to the next possibility.