Complex sentence: Chmielarz sold between 4,000 to 6,000 copies by mail at a time when just a thousand or two thousand units sold were considered a major achievement as even foreign Western hits had rarely achieved that level of sales, and as the market was still dominated by piracy.
Split into simpler sentences: Chmielarz sold between 4,000 to 6,000 copies by mail at a time when just a thousand or two thousand units was considered a major achievement. Even foreign Western hits had rarely achieved that level of sales, and the market was still dominated by piracy.