Difference between Sincere and Believable

SINCERE vs BELIEVABLE: ADJECTIVE

Honest; free from hypocrisy or dissimulation.
Being in reality what it appears to be; having a character which corresponds with the appearance; not falsely assumed; genuine; true; real.
Whole; perfect; unhurt; uninjured.
Pure; unmixed; unadulterated.
Earnest; meaning what one says or does; truthful.
Meant truly or earnestly.
Open and genuine; not deceitful
Pure; unadulterated.
Being without hypocrisy or pretense; true.
Not feigned or affected; genuine.
Characterized by a firm and humorless belief in the validity of your opinions

Sound; whole; unbroken; without error, defect, or injury.
Pure; unmixed; unadulterated; free from imitation; good throughout: as, sincere work.
Having no admixture; free; clear: followed by of.
Unalloyed or unadulterated by deceit or unfriendliness; free from pretense or falsehood; honestly felt, meant, or intended: as, a sincere wish; a sincere effort.
Free from duplicity or dissimulation; honest in speech or intention; guileless; truthful; frank.
Morally pure; undepraved; upright; virtuous; blameless.
Synonyms and Fair, Open, etc. (see candid); Cordial, Sincere, etc. (see hearty), unfeigned, undissembling, artless, heartfelt.
Open and genuine
Not deceitful

Heart whole, Bona fide, Dear, Serious, Solemn, Devout, True, Unfeigned, Earnest, Fervent, Wholehearted, Cordial, Honest, Genuine, Heartfelt

Unlikable, Implausible, Likeable, Likable, Creditable, Incredible, Reliable, Unbelievable, Heartfelt, Trustworthy, Sincere, Presumptive, Likely, Credible, Plausible

Heart whole, Bona fide, Dear, Serious, Solemn, Devout, True, Unfeigned, Earnest, Fervent, Wholehearted, Cordial, Honest, Genuine, Heartfelt

Unlikable, Implausible, Likeable, Likable, Creditable, Incredible, Reliable, Unbelievable, Heartfelt, Trustworthy, Sincere, Presumptive, Likely, Credible, Plausible

Sincere wishes on your anniversary, Mom and Dad!
One integral and sincere confession within nine days.
Please believe in my feelings of sincere friendship.
Please be reflective and sincere in your discussion.
Crown patrons has often been read as sincere.
Finallymy most sincere thanks to my wife Lauren.
He is childlike, simple, humble, sincere, and forgiving.
Heather Price is sincere, laid back and professional.
Those sincere men who told them so believed it because an earlier generation of sincere men had told them the very same thing.
Her narratives combine sincere anxiety and sincere compassion.

Judge and making the Bible even more believable!
Doing so often makes the impact more believable.
Now this theory strikes me as believable, certainly.
It must be believable and reflect shared values.
Leave out anything that is intrinsically not believable.
Heather Justesen knows how to write believable romance.
We established a believable relationship, no neighborhood witnesses.
Mary Austen is believable and holds emotional weight.
This comes from simple logical analysis and was entirely believable when I wrote it a decade ago, and remains entirely believable today.
Physics is well placed to supply believable ages, or at least a believable range of ages, for most of these events.