In my world, there is a race of shapeshifting creatures, capable of convincingly looking like normal humans in order to lure them and prey upon them. These creatures, however, are non-sentient and non-conscious, a bit like the aliens in Peter Watts' Blindsight. So what do they use to trick their human preys? They use telepathy.
These creatures can read minds and can therefore act like their prey thinks they will act. If one of these shapeshifters takes the form of a person and you stumble upon them, they will act like you expect, hypothesize or hope for, all depending on what you are actively thinking in that moment. They can handle grammar and syntax just fine by talking like you form words and sentences in your mind, and they can process all the needed info just as fast as you think them.
Their telepathy also allows them to pick up on the preferred answer that their target hopes for, so if asked "are you a shapeshifter?" the answer will be invariably negative, unless you want them to be one (in which case you probably just want to commit suicide-by-shapeshifter, because no one hopes to meet one). Their answers will always be soothing, reassuring or enticing, simply due to them being "programmed" to go for the answer that makes you feel the least fear and the most curiosity or attraction. At the very least, their answer will be as non threatening as possible given the current thoughts of their prey. Basically their telepathy allows them to communicate a bit like a Chinese room, again, just like in Watts' novel.
They have a few limitations, chiefly that they can only use their telepathy on one mind at a time and that they can't read anything other than what the person is actively thinking. However keep in mind that it's borderline impossible to have a conversation with someone without forming expectations or thoughts on their answers in your mind, which the shapeshifter will immediately use to its advantage. They can only shapeshift into humans or human-like forms, both by imitating a person they have seen or preyed upon or by picking something out of the mind of their next victim if they are thinking about someone in that particular moment.
Other than this, assume that their telepathy can't be blocked or jammed in any way and that their shapeshifting abilities are perfect, so that no physical evidence can be used to unmask them. However, people do know that they exist, though these creatures are not common enough to be a constant worry. Enough to get suspicious if someone acts strangely or looks out of place but not enough to be completely paranoid.
In answering this question assume that no relevant technology is available and that no large scale countermeasures are possible, such as anti-shapeshifter laws and customs, humans have only their own individual wits on a case-by-case scenario to save them from becoming a shapeshifter's next meal. Also consider that shapeshifters only target humans that are alone or with just another person, so they never approach more than 2 people. If the shapeshifter manages to be approached at social distance for more than a few seconds, there's no escaping, the shapeshifter will easily overpower up to 2 humans.
With all of this said, what kind of tactics and tricks might a human pick up to spot a prowling shapeshifter effectively?