I want to buy a bus ticket (from Belgrade to Podgorica) online at https://busticket4.me/. However, I wonder if this site is reliable (maybe it's just a scam, maybe they will take my money and will not sell me a ticket).
Does anybody have any experience with them? Has anybody succeeded to buy a ticket from them?
As pointed out by @chx they satisfy the general criteria of a real company.
They have an active Facebook page with recent reviews
Their Android app has plenty of reviews and was recently updated
Their contact page lists a physical address
Their parent company is real and the owner looks like a real person (please Google their name by yourself)
Whether or not they're reliable is primarily opinion based and is not a good fit for a Q&A format.