QUESTION #1
What is the best way to let someone down after you've had several good dates, but then realize that you are not a good match - no chemistry, different goals...
When rejecting someone, diplomacy is key. You don't need to be specific. In fact, I advise against it. All you need to do is send them a text or email and say, "I've really enjoyed getting to know you, but I'm not feeling what I need to feel to continue dating you. I wish you the best."
That's it. That is all you owe them at that point. You are not obligated to go into any kind of detail about why you're not feeling it. If they respond asking for clarification, you can be a bit firmer and say, "The chemistry isn't there for me. I really don't wish to discuss this further."
Set that boundary. If they respond, block them. You showed them the courtesy of an explanation. That's enough. Any further attempts by them to gain clarity are inappropriate and should be treated as such.
QUESTION #2
My last Tinder match wouldn't stop messaging me even when I told him I was busy with work. I finally told him I'd changed my mind about dating because of the corona virus. I figured that was a safe excuse most reasonable people would accept. He got mad and accused me of being on the app for attention and said some other nasty stuff. Should I have said anything? I don't think I was rude.
You weren't being rude. He was just butt-hurt because you didn't want to go out with him. The problem with people like this is that they choose to be obtuse rather than read between the lines. Most socially adept adults know that "I'm busy with work" is code for "I'll respond/contact you when I have a free moment." In a case like this, when someone refuses to read the room, the other person is now put in a situation where they have to be explicit. Nobody wants to do that, which is why so many people ghost.
The keys to rejecting someone without dealing with retaliation or blow back is to follow these tips:
Don't engage if you're fairly certain you and they are not a match. It's great to give the maybes a chance, but if you aren't even the tiniest bit curious about someone, don't respond. Forget about "being polite." If you're not interested, do not respond. Engaging in any way opens the door to further conversation, some of which might be hostile or combative. Keep the door closed unless you're willing to walk through it.
Don't respond right away. Replying immediately to a message conveys excitement. Stagger your responses in a way where you're not being dismissive of their time but you're also not matching their enthusiasm. This is also a good way to control the pace of the e-lationship.
Don't give them your phone number or any alternative contact info. Exchange of anything identifiable - your last name, email, phone number - should not occur until either you've set a date or had a first date. Remember, you don't want to seem more interested than you are. Keeping communication to the dating app sends a clear message: I'm not quite ready to take this to another level.
Don't blind side someone. If you've been messaging back and forth with someone a one hundred and eighty degree turn will seem sudden. A lane switch like that will give away that you're lying. It will also catch them off guard, which in turn could make their reaction more severe. If you're on the fence about meeting them, keep your messaging to a minimum. The more time you invest, the more interested you will appear.
Finally...
Don't prolong the conversation. Either take things to video chat or meet offline. Determine if there's chemistry as quickly as possible. The longer you exchange messages or keep things online, the more likely it is someone will say something that turns the other person off. Someone truly interested and available is going to move things off the dating site in an expedited fashion. Those who don't are usually - if not exclusively - wasting your time.
Good luck!