Reverb selling fee
Reverb's official fee page says the selling fee is 5% of the total sale amount including shipping. Reverb lists a minimum and maximum selling fee by currency, including a $0.50 minimum and $500 maximum for USD.
Payment processing
Reverb Payments lists 3.19% plus $0.49 for standard sellers and 2.99% plus $0.49 for Preferred Sellers. Processing is calculated on order total and can include tax.
Extra fees to model
Depending on the order, sellers may also need to model Reverb Bump fees, cross-border processing, currency conversion and shipping labels purchased through Reverb.
Example
For an $850 guitar with $45 buyer-paid shipping, the 5% selling fee is $44.75. Standard processing at 3.19% + $0.49 on $895 is about $29.04. COGS and label cost determine the real profit.