You could be missing an opportunity here .

There is no need to treat this kind of request in any different way than any other sales lead . Tell them simply that this is what you do for a living and tell them your rates and your availability and you would be happy to try and fit them in your schedule if the cost can be agreed . Then see what they say . They will either engage in some form of negotiation or not . There is no downside here. Either you will secure a booking you did not expect to get or not .

Be truthful , be clear and be polite . You are professionals so be professional and you will be treated like one .