Michael, Dave has some good suggestions above, and I think Larry's point is good. In other words, is playing this particular horn enjoyable, or not.

There was a fairly short thread (link below) about testing euphoniums, and in that thread Dave links to an article he wrote on this forum that has a lot of good, detailed thoughts on testing a euphonium.

http://www.dwerden.com/forum/showthr...s#.Y1FVwPzMI2w

If it were me, I would warm up playing easy long tones, 1-octave scales or scale fragments, and 1-octave arpeggios to get a sense of the horn. Once comfortable with it, I would probably do some 2-octave scales and any favorite tunes/excerpts that you know. Bring some sheet music with you. Try something slow/melodic and something fast/technical. For the scales, vary the articulations (slurred, accented, staccato, etc...) to get a sense of how it responds.

If you have a euphonium that you are currently playing on, bring it along to compare. If possible bring a musician friend that can give their opinions.

When I got my 3-valve compensating Besson New Standard (made in 1976), my very first impression was a bit of disappointment in the sluggishness and noisiness of the valves, but once I cleaned them, oiled them, and replaced the felts and springs it was totally fine. I just wanted to share that in case you had a similar first impression. Try to focus on the sound and enjoyment/ease of playing it, and if the valves just seem noisy it may be a simple fix with some Mead Springs and fresh felts.