The B710 was Revox's entry cassette deck; it shares the B215 transport family.
Cassette deck: check belt/idler set and head wear before valuing.
Marks that can be entered for this maker: Serial number, Model / catalogue number, British capacitor code (Hunts, Mullard), Japanese capacitor code (Nichicon, Chemi-Con, ELNA), EIA component code, Chassis / platter stamp, Version & era marker.
The introduction year is not documented, so the model narrows nothing.
Sold-price aggregates are not collected yet, so the archive gives no figure — condition, originality of the transformers and a documented recap move this model more than any list price.