Finding the right rug is probably not different from finding an authentic jewel. You need to have an eye for the detail to know if you are investing in something worthwhile, or at least if you are not too concerned about collecting a rare antique then making sure that you are being asked for the right price. There are many sites that provide affordable rugs online.
If you are really determined to choose a great work of art, which would not just be authentic but also be of the highest quality, then you need to devote a fair bit of time in examining a single rug and comparing it to several others.
It would not be wrong to adopt the approach of exploring rugs in the way you examine works of art. A single Oriental or Persian rug could take hundreds or even thousands of hours of craftsmanship and it is only fair that it demands a little attention. However, you could easily check the modern rugs without spending too much energy.
It hardly needs any elaboration that a hand-sewn rug and a machine-sewn piece differ greatly in their detail, and therefore, value. That depends on your décor choice, preference, and purpose of the rug that you are choosing.
You should at least take enough time out to find out as many details about the rugs as possible and while you may consider finding a reliable dealer of rugs online a daunting task, this is a good standard to judge how much you can trust them. An experienced, knowledgeable, and dependable dealer will always have answers and patience for your questions, and would offer clear and detailed pictures of the rug.