There are many factors that should be taken into consideration to figure out the value of a website: revenue, traffic, age. While revenue is a result of traffic, rankings, etc, then you can guess a value just with it. Most websites are selling for 10-12 times their monthly revenue, but there are some rules that you might want to follow to not being tricked by website flippers.
The most common technique I found among website flippers is that they try to convince you to value the website just by knowing only the previous month income, or less. They will say: “This website made me 100$ in the last 15 days, this means that if you buy it with 300$ you will get the money back in 1 and a half month”. If that was so easy, why he wanted to sell the domain instead of waiting 1,5 months to get that money ? This is what guys like him does. They don’t have to lie you, they tell you the truth, but only the parts that are at their convenience.
If a website is less than 6 months then it is a bad thing to consider buying it for 10 times monthly revenue. The traffic is probably forced ( redirection from other websites, overuse of social media ) or it is brought. Nowadays, you can buy tens of thousands of visitors with few bucks. They are real visitors, but those people are not interested in the content. But, what is most important to you is that they will be all gone after you buy the website.
They will continut the communication with you and they will “try” to help you, but when it will come the question: “Why does the traffic dropped ?”, they will say that the you did not put all the marketing efforts that they have done before selling and since you are not as experienced you will think that this is the reason. If you want to learn more about how to value a website you should read on this website and maybe ask for a quote.
Disclosure: Some of the links in this post are "affiliate links." This means if you click on the link and purchase the item, I will receive an affiliate commission