Sell-side analysts took a stick to Commonwealth Bank yesterday, after reviewing its September quarter earnings update. While only one investment bank, Citi, downgraded CBA to a "Sell", most analysts cut their earnings forecasts for the bank.Analysts did not like the fact that Commonwealth's costs grew at a greater rate than its revenue during the quarter; that its net interest margin fell; that its trading income was weak, and that its Tier-1 capital ratio came down a little.Citi changed its recommendation from "Neutral" to "Sell" and set a target price of A$46 on the stock (yesterday's close was $48.62). Apart from the general observations mentioned above, Citi said the bank was struggling with lending share and was more heavily exposed than other banks to the out-of-favour wealth management sector.Citi said that "management has promised better market share performance this year but there are no easy gains."JP Morgan maintained an "Underweight" recommendation on the stock and downgraded its earnings forecast for 2011/12 by 1.8 per cent.Deutsche Bank said: "Commonwealth Bank reported a slightly soft first quarter cash earnings result, mainly impacted by lower trading income. While comments from Commonwealth and other major banks suggest that market trading conditions are starting to recover, we have reduced our second-half trading income forecast by about $20 million."Deutsche maintained a "Hold" on the stock and downgraded its 2011/12 earnings forecast by 0.12 per cent.UBS maintained a "Neutral" recommendation. It said: "Although the $1.75 billion net profit was broadly in line with expectations, pre-provision profit was flat at around $2.7 billion. This was a result of margin pressure and weaker trading."Credit Suisse downgraded its 2011/12 earnings forecast by one per cent, reflecting lower revenues, higher costs and the normalisation of the bad debt charge. It retained a "Neutral" rating.It quoted CBA's comment that maintaining positive "jaws" (revenue rising at a greater rate than costs) was a "real challenge" at present.Goldman Sachs maintained a "Hold" and downgraded its 2011/12 earnings forecast by 1.2 per cent.