Is there such a reliable source so I can identify the stones by myself?
Most semi-precious stones are various forms of quartz or silica (e.g., agate, citrine, etc). Quartz is very hard and will scratch glass. It is hard to scratch quartz. Therefore, this is a non-destructive way for identification of quartz. It usually takes a really good polish that lasts. Hardness is pretty much the best way to identify quartz and other varieties of silica, because they visually look all so different.
Apart from quartz, there are several things which are unmistakeable. Watermelon tourmaline, for example. But if you got something which is not quartz and is not obviously something else, it becomes extremely hard to teach yourself to identify it. Even experienced geologists will have a difficult time identifying the stone without resorting to (somewhat) destructive and expensive methods such as XRD, XRF, EDS, etc. The dealers often don't even know what they have. They bought it from someone who bought it from someone and who knows whether the miner actually knows what they're mining.