Well, your concern over the matter is correct but prior to that one need to understand the basic purpose of astrology. For me, it is a science of probability and nothing can be predicted with hundred percent guarantee. Those who predict with hundred percent guarantee are nothing but poor and ignorant persons trying to invite unjustified attention for their selfish purpose.
Before approaching for astrological advise; one must understand the importance of Karma (Deeds). If everything could be predicted or decided mere on the basis of astrology or some other science/art; the very purpose of life is defeated.
What astrology can offer:
An example overhere will suffice to clear the situation. Suppose you own a car and need to travel. Astrology can provide you some insights in connection with the condition of the roads, the visibility, expected traffic situation, expected behavior of the other road users, info. regarding accident prone spots etc. Astrology can also provide you some information regarding the condition of the vehicle you may be using. But, you are the ultimate Driver of the vehicle; and if you have got proper understanding of driving skills or you so decide to learn the art of driving properly; you will always be able to use the provided information for your betterment. That is, you will drive slow and very carefully over the accident prone spots, you will pay attention to the road signs, follow the traffic rules, drive more attentively at conjusted strechs and avoid driving during uncomfortable or unfavorable situations like lack of visibility or bad weather etc.
Therefore, the basic purpose of astrology is served when the one is informed about future insights regarding expected environmental conditions in specific areas of life. And until and unless, one is capable of understanding and digesting the information there can be no use of astrological advise; no matter what stone you use or what mantra you recite or what remedy you perform.
There are many ways of performing remedial measures and use of gem stones is one of them. Why it is so popular; because it allows one to have astrological benefit without much bothering. No doubt, the Mantras and vedic Rituals are the most effective among all remedial measures; but in todays life it becomes slightly difficult for one to follow the rituals appropriately. Further, Mantras need to be activated by both (i.e. the one who is giving the Mantra and the one who is receiving it) with proper rituals and mere reciting of a Mantra (without following the proper ritual) is of no use (Except Shabar Mantras).
If one is unable to afford the gem stones; the substitute remedies have also been provided. But, one needs to be consistent with his approach for receiving help. Like medicinal line, more doctors one approaches for a specific problem; the more confusion one may have.
You can post your birth details and problems for further information on your chart. Problems are a part of human life which helps him in development and achieving the ultimate goal of his life.