Just because someone calls themselves a professional fishing instructor or some other type of self-styled expert doesn't mean they really have any type of remarkable insight. Often it simply means they know one type of fishing or patch of water better than anyone else. Sometimes it simply means they couldn't get a proper job and are trying to make some money on the side. Making a few schillings doesn't make everyone a professional in the most helpful sense.
That said, there are plenty of things you can learn from those with specialized knowledge and old-timers, alike. This is especially true when you're looking for information regarding the behaviour of a particular fish in a certain water or area. Such information is best found through experience, and many guides use such experience to work as a professional fishing consultant. Angling techniques suggested by such individuals are often at least worth a try, especially if you're new to the area.
In somewhat less direct situations, such as columns or television shows that feature any number of people who would suggest their advice is worth listening to because they are professional fishing guide, the tips are usually a bit less useful. Generalized advice is very often just that. In fact, most shows are more useful as entertainment and travel advice rather than valuable fishing information.
It is also worthwhile to consider the many endorsements that pays the rent of a typical professional fishing expert. Angling products that don't make anyone any money, such as using "boilies" or maize for baits may be the best solution, but won't be getting much play by the experts, since there's no economic incentive to do so.
Perhaps the professional you should have the least confidence in is the braggart down at the local pub. Closely related to the people who loudly announce they've got very important jobs with the Scotland Yard, such so-called expert's advice is often best taken when you do the opposite of what they recommend.
In contrast to all the "fish tales" of those who are not professional, the real pros tend to be somewhat more demure folks who sometimes need persuading beyond pound-notes to get them to spill some of their sage wisdom. Often, one is best served by taking a more relaxed approach of observation and a few pointed questions rather than expecting to get fully "schooled."
Generally, the best advice is dolled out one golden nugget at a time unless you're willing to pay big bucks for it. Patience is probably the best advice any one can give you regarding how you should best go about learning more.