Psychology's body of knowledge consists of findings that are inconclusive, because there is no quantifiable way to measure the mind accurately. There are inconsistencies in human behavior that vary not only from person to person, but within an individual as well. What's more, it is also difficult to replicate the same results between experiments. As such, coming up with an accurate method of measuring the mind is impossible. Psychology also lacks a generally agreed-upon definition and terminology. Some call it an art, others call it a science of the mind. There are also many branches to consider: Clinical, cognitive, developmental, evolutionary, etc. Which one is the defining psychology? Psychology cannot be a real science with these issues in play.
There may be inconsistencies in the terminology, methods, and results of psychological experiments, but it is not the only field of science in which this happens. Chemistry and drug discovery, for example, lack a definition as to what a "druglike" molecule is. In any field of science one will find debates and inconsistencies. No science is perfect.
[P1] There are no reliable methods to measure the mind. [P2] Results don't replicate reliably between experiments. [P3] There is no clear definition of psychology. [P4] Psychology's findings are inconclusive and therefore it is not a real science.
Rejecting the premises
[Rejecting P1] For psychology's purposes, there are valid measures in place for studying the mind. [Rejecting P2] Replications don't always work out, but when they don't, it indicates a poor effect of the experiment, which is a valid result. [Rejecting P3] Psychology is defined by Merriam-Webster as "the science of mind and behavior." [Rejecting P4] There are many sciences in which the findings are inconclusive. This does not invalidate psychology's status as a science.