Two versions of this, and they need opposite handling.
When they want it and you do not
The pressure here is heavy, and the argument that usually gets made — "what is wrong with them?" — is impossible to answer, because often nothing is wrong with them.
The useful move is to stop defending your reasons and describe the outcome instead. Not "I don't like him" but "I would be agreeing to something I don't want, and you would be watching me be unhappy in it."
Most parents, told plainly that a marriage would be unhappy, stop pushing. They are not trying to make you miserable. They usually believe you are being unnecessarily particular, and that certainty comes from thinking your objection is trivial.
And give them something. A flat no with no alternative leaves them nowhere. "Not this one, but I will meet the next three" keeps everyone moving.
When you want it and they do not
Harder, and the instinct — presenting it as settled — is usually the thing that causes the refusal.
Find out what the objection actually is. Stated objections are often stand-ins. "Different community" may mean *what will my brother say*. "Too far away" may mean *I will never see you*. You cannot answer an objection nobody has admitted to.
Let them meet. Categories are easy to refuse; people are not. Most parental objections soften enormously once the person is in front of them being ordinary.
Do not make it a contest. "Them or me" forces a choice, and families that are forced tend to choose badly and then live with it for years. Almost nobody who won that way is glad they did.
Be patient in weeks, not years. Many families come round in a month or two. Very few come round in a day, and being pushed hard on day one makes the second month worse.
What both situations have in common
The argument is rarely about the match. It is about who gets to decide, and that argument has usually been running quietly for a decade.
Saying that out loud helps more than any amount of arguing about the person. *We are not really disagreeing about him — we are disagreeing about whether I get to choose.* Families that get that sentence on the table usually find the rest easier.
Most of these end in agreement. The ones that do not are usually the ones where somebody made it a test of loyalty.