In most commercials,most companies present themselves as market leaders.what makes a market leader?shouldn't there be a control over such claims.

YES,,BUT THE TRUE MARKET LEADERS OF THE INDUSTRY MUST STOP THEM.

Yes, there should be a control so that the correct and right message should be provided to the public.

Market leader co. it called for the co. witch catch a biggest percentage of the market and also other co.s waiting this co. to select the sealing price

They might claim leadership on different parameters- Customer satisfaction index, top line achieved, bottom line etc. I know of a company in the business of manufacturing Inverters claiming to be No2 and then warning No1 company to watch out to them being challenged. Any unethical claims must be definitely checked as it only ends up misguiding the customers

If you are referring to commercials on TV, then I guess such control is already existent by many organs overseeing advertising and ruling on ads qualification to be displayed to the millions of followers of mass media, in terms of obscene, offensive or deceitful messages. Companies, especially the big ones, are very careful about TV-ads, also newspaper ads.

"Market leader" is often read on company websites, especially these with a small or new niche, of which market leadership cannot really be established or double-checked by the average consumer/customer. In such case it is the job of Consumer Protection Organizations to provide up to date info about such providers/producers. This actually happens in some countries.

I beleive that there must be control over commericals to ensure that correct fare messages are being sent.

A market leader is the one who succedded to provide the value perceived by its target customers.