When you have no idea of a potential value of a domain, and need some form of benchmark, then sites like estibot/valuate and domainindex are as good a place to start as any as at least their valuations are based on a form of logic. Whether that logic is similar recent sales. a valuation based on CPC costs and search volume or some other completely unrelated factor, as long as they haven't screwed up determining the words contained in the domain, the process behind their valuations should at least be consistent when applied to and compared with other similar domains valuations. It won't be an accurate valuation of course but how could it be? An accurate valuation will not be known until the domain actually sells, and even then how accurate it is will be affected by how skilled or motivated both the salesman and the buyer were.
A seller using an estibot valuation to support their sales price doesn't necessarily believe that is the definitive value, but does know that buyers often need some form of independent justification of the price quoted to reassure them that they are not over paying and in that regard, these sites do help, even though they often differ wildly in their valuations.
A case in point being a 11+ years old domain I just "valued" recently and have for sale on Flippa (cctvsex.com). Estibot values it at $430, but domaindex values it at over $7,000. One of them may be right, but most likely both of them will look like they were wrong even if they were right because I have set a reserve way below those figures and chosen to sell it on Flippa at a time when that platform is starting to look overly saturated.
Bottom line, even if the domain sells for less, it doesn't necessarily mean that these valuations were wrong.
