Lawyers are always considered the last hope of any accused person. Whether you will be acquitted or convicted lies on who defends you in the court. There have been many reported cases of lawyer lying even in the court of law, all to win the case.
The belief lawyers do lie is something real, in fact with many lawyers building a reputation of 'I must always win', they do everything in court to ensure they win the case, though this is unethical and is always as a result of lack of skills and professionalism. Lawyers do lie more than a normal person. We have cases where lawyer would tell his client he would win a case with every assurance but ended up losing it.
This problem about them can be corrected if heavy sanction can be imposed on any lawyer caught lying. However, most times people call lawyer liar because they don't understand legal profession, because every lawyer will always put his best to convince the court about his client