They block the shopping streets and their music is terrible. There are no empty streets in the Netherlands on a Saturday and there is nothing more depressing than a Eastern European on an accordion.
Btw, here in Serbia (what you'd probably call Eastern Europe :), accordions are pretty rare (I guess they all went to Netherlands :)) other than in gypsy bands (but they rarely play in the streets other than when following weddings around), but violins (usually students), keyboards and guitars (number one, duh) are most common, but you get to hear a trumpet or a flute too. We are just classy like that (or there might be a musical school or two nearby in the part of Belgrade I see them in ;).
Eastern European music schools , and particular those with folklore specialties, have had a long history of master classes. It is often that one can find street talent with proper education, just because music industry pays very little in Eastern Europe.
It seems to me that in Western Europe you find mostly dégénérâtes and hippies with no formal music education at all.
One can know the difference
only if he has lived in Eastern Europe.
Perhaps the better Eastern European accordion players stay home. I used to visit Krakow often on business and really enjoyed listening to musicians playing in the main square. Also it wasn't just accordion players, there were all sorts, amateurs, music students, professional musicians playing a wide variety of instruments and styles.
It was worth having some cash to put in the bucket.