After interviewing all founders who sold the project, I always asked one question. "What was the actual selling price?" And 100% of founders replied the same number as it was in the asking price.
In my opinion, prices are pretty accurate on the platform. However, you should count the work done(hours spent), marketing activities, tech expenses(domain, hosting), maintenance, customer support.
Every case is unique, so it's hard to tell about all listings at once.