At times I have been skeptical of the Reformation idea that everyone should read their bible, because the bible is difficult to understand, and is arguably something that should be left to competant experts - and even they will make serious errors at times. In most fields, eg quantum physics, medicene, engineering etc we do just "believe the experts" and don't try and do it ourselves. But in most fields the experts have an extremely high level of agreement on major issues, whereas in biblical interpretation the experts almost always have severe disagreements, and experts can be found who support almost any given view about what the bible says.
So how does the man-in-the-street know which experts to believe? Generally people just believe their own tradition - they believe what their pastor tells them. A person born to parents who go to a Catholic church comes to accept the expert opinions of their own group's teachings and a person born Reformed likewise. This is, of course, hardly a practice that leads people to actually believe what is true - it is no better than tossing a coin. The chances that the denomination you were born into is correct, rather than any of the other 99 denominations all claiming to believe biblical truth is only one in a hundred.
It disturbs me when I see denominations teaching their adherants that "We are right, everyone else is wrong. Our experts are the best. Only our doctrines are biblical truth." I see people who belong to those denominations being indoctrinated into believing the Truth of their pastors teachings. These people then are taught to go out and teach the Truth to others and convert them into the fold of True Christianity (ie that denomination). In reality, these people haven't engaged in any careful unbiased analysis of biblical doctrine, and are just parrots who have been taught to repeat the phrases their masters have given them. If their doctrine is true, then it only due to luck. I find this idea, which I will here coin "denominational-discipleship" quite scarey. Through indoctrination it promotes proud and arrogant certainty and exclusivism that is not at all backed by any corresponding accuracy, evidence, or reason. I'm sure we can all think of people we have met who have been adversely affected by this process, and it is not a good thing.
But what this means is that picking experts at random (since what denomination you happen to be born into is random) and treating them as gospel is not a good idea. There is no reason why one randomly picked expert should be better than another. Some average Christians might listen to a few experts and go with the one that "sounded best" (according to some arbitrary measure of 'best'). But of course, as we all know, academic ability and rigour does not necessary correlate with rhetorical ability or debating skill. Good speakers aren't always good scholars and vice versa.
I believe it comes down to this: Where the experts disagree and tread lightly, only fools run in and claim they have the certain answers. It is the responsibility of the man in the street to not go claiming they themselves have the true and correct answers on a subject where the experts widely disagree. If someone has no time or ability for proper study, then it is irresponsible to put their own conclusions ahead of expert opinions, nor is it responsible to choose one set of experts over another without reason. If a person is not prepared and able to make the effort to carefully explore the expert opinions being offered, the evidence for them, and the research behind them, then that person is not entitled to have a firm or expert opinion.
Thus the simple answer is that that average Christian ought to accept the opinions of all the experts taken as a whole in their diversity. On subjects the experts disagree, then the person should be tolerant of a diversity of opinions. On subjects where the experts broadly agree, then the average Christian ought to accept the opinion of the experts. The average Christian then needs to be open-minded and tolerant of the wide variety of opinions that are held within Christianity. The man in the street should neither pick certain experts at random and take their word as gospel, nor should they take their own interpretation of the bible as gospel. Rather, they should just get a basic idea of the variety and types of different opinions that the experts have, accept all of them as possibly true, and then go no further. Sadly, few resources are available to easily facilitate this task.