When someone tries to say someone else is faking DID, it's called "fake claiming". This is generally an abuse attack by someone on a victim. It's nearly impossible to know in a social media exchange whether or not someone has or does not have DID. We should neither diagnose nor fake claim others without a license.
To be clear, the only way to fake DID is to do so deliberately. The connotations for faking imply pretending by way of deception and intent to deceive. Some people pretend to have DID above-board/deliberately (an actor for a role) and that's not faking; that's portraying a role.
There are folk who are misdiagnosed, whether self-diagnosed or professionally diagnosed. They're not faking; they're misdiagnosed or mistaken. It's not common to be misdiagnosed or mistaken as having DID when one does not; there are very clear criteria and professionals are exceptionally reluctant to diagnose DID in general, some outright refuse to diagnose it. So the likelihood of someone getting an actual DID misdiagnosis is extremely low.
Note that neither factitious disorder nor "imposter syndrome" are faking DID. Imposter syndrome is where someone HAS an issue, but has insecurities or reality distortions that make them FEEL like they're faking it. Like derealization/depersonalization (common for people with dissociative disorders, especially DID) can make you feel like an imposter, even though you're 100% legit.
Factitious disorder is a diagnosable disorder where someone has trauma and deep insecurities and latches on to various disorders to try to explain their issues, but they don't actually have the disorder in question. They're not trying to deliberately or consciously fake anything. Rather, they have a deep need for an explanation of what's wrong with them and are very confused and "trying anything on" to ease their anxieties. It encompasses the issue formerly known as Munchausen Syndrome. It is itself a legit disorder but the person is convinced there's something wrong (they're right) and grasping at anything to explain it (often wrong).
Then there's just faking. Which is different from acting or method acting — so long as someone is portraying a role explicitly/on screen/stage it's tentatively OK (better if an actor with said issue/disorder plays the role(s)).
People faking deliberately for attention do not have factitious disorder, or imposter syndrome. And they're not just acting on-screen/on-stage. Reasons folk may fake DID abound, but some common thoughts on the issue are either a) seeking attention deliberately (as opposed to factitious disorder where it's not deliberate) or b) to infiltrate the community as either a troll or to undermine/attack a vulnerable community such as doxxing folk or to seed strife/division in the community so that support communities fall apart. The former (a) is selfish and probably can be safely ignored in the community. Folk will eventually figure out that having a DID diagnosis is not all it's cracked up to be and look for another way to get their needs filled after they lose jobs or respect or friends look at them in fear etc. We want to lose the stigma, but the idea that someone wants "attention" by having an extremely stigmatized disorder is almost laughable. What type of attention would they like?
However the 2nd case (b) is of great concern to the community and reinforces divisiveness and creates controversy, folk have been suicide-baited (sometimes successfully), attacked in their homes when doxxed, lost jobs, family, income, housing, etc. due to the attacks of deliberate chaos-sewing infiltrators in the community.
I suppose a 3rd case worth mentioning is when someone deliberately infiltrates the community to collect victims. People with DID often have poor boundaries and may have alters who seek out unhealthy attachments and relationships. Perpetrators have come into the community to collect victims to victimize privately or folk have (whether intentionally or not) formed cults or cult-like attachments with members they have gathered from within the community.
Unfortunately most fake claiming or lists of "you may be fake if" cause a lot more harm than good. We should really be on the lookout for deliberate perpetrators and folk looking to cause trouble, and protect our more vulnerable community members from being exploited or cornered by bad people. Everyone else will get sorted out eventually on their own without community intervention. If we provide amazing support avenues and treat community members with respect and compassion, then if someone discovers they were wrong they will be left with an amazing impression of how supportive our community is, and can guide legitimate folk needing our community to us to get the support they need.
So just look for assholes, and help educate new community members on good netiquette, safety guidance, and preventing folk from either oversharing details of their life (that can lead to doxxing etc.) or prevent them from dealing 1:1 with potential cult recruiters or abusers in DMs etc.