This looks to be a Besson manufactured before they moved to Germany. Many Besson euphoniums of the late 90s and early 2000s had quality issues while the company was experiencing financial difficulty. My first professional euphonium was a Besson Sovereign 967 manufactured in 2002, and it developed a lot of red rot along with having very sharp intonation in the 5th partial and higher. Any potential buyer would be wise to ask for the serial number and find out when this euphonium was made.
James Kircoff
Genesee Wind Symphony - principal euphonium (Adams E3 Custom .60mm yellow brass bell w/ K&G 3.5)
Capital City Brass Band (2019 NABBA 2nd section champions) - 1st baritone (Besson BE956 w/ Denis Wick 6BY)