You should create some quick responses for situations like that - and respond as soon as you see the message. Just say something friendly – that encourages the buyer to leave you a more detailed message. Something like:
“Hi there! Thanks for connecting. If there is anything specific you would like to know about my gig, feel free to ask.
Done! You have left a response - and now the ball is in their court. If they DON’T get back to you, that’s okay - because you have already responded, so your response rate won’t be affected negatively.