Quick answer
Select the Message Seller button on the listing to start a message thread between you and the seller. The majority of sellers on Reverb respond to messages within 24 hours.
Since Reverb is a marketplace full of unique sellers, Reverb staff is unable to answer questions about specific item details.
Further reading:
How do offers work on Reverb?
How do I contact the seller of my Reverb purchase?
What is Reverb's return policy?