The practice of investing money in companies listed on any of the stock exchanges with or without the advice of a stock broker can be risky. On the other hand a lot of money can be made through stock brokers advice. With that being said you should carry out your own analysis of the stocks being recommended by a broker as any advice given is purely subjective and based on past performance. This does not mean the trading advice is without foundation but some brokers can fail to predict what is going to take place even with giant warning signals flashing ahead like the sub prime mortgage fiasco, oil hikes, Greece economic collapse and so forth.
It is also a good idea to keep in mind that stock brokers/advisors earn a small percentage from recommended stocks and it is tempting for stocks to be quickly recommended even though they have not been thoroughly assessed, researched globally or the fundamentals such as P/E, cash flow, assets, debt, examined. And it is also worth knowing the background of your money manager especially with regards to the number of years experience gained and if they are personally successful with their own trading accounts.
Despite all of this and you have done your due diligence, the company you have invested in is solid with high profitability ratios, market fluctuations can still leave you with your trousers down and with no where to go except to endure the pain of hanging on and hoping the stock will regain its value. Therefore, in my opinion it does not make any sense in buying stocks, funds, equities, etc based on yours or other peoples opinion even if they are experts at predicting the future values of stocks. So what is the alternative and why are some people more successful than others with trading? The answer is probably based upon knowing the science of probability and statistics or having a well researched long term plan based on overall solid growth and performance with great companies.
One of the ways to win quickly with stocks, currencies, commodities is to play the numbers game and make the predictions non-subjective by using probabilities. This can be done with a high number of trades in different markets while only risking 3-5% of your capital. However, this is easier said than done and you would most likely require computer software to work out the statistical probabilities using numbers and charts.