With Craigslist, there are no holds, no dibs. I do not hold a bike for anyone largely because of the huge number of absolute flakes. First come, first served.
I have however changed my policy if I get a deposit from the buyer to show that they are serious about the purchase
I also always put my number in my ad

There are a lot of flakes on CL, both buyers and sellers.
I've sold a couple bikes and some parts.
Initially, I would give the potential boyer my home address on first contact. After I realized that probably only 1 out of 3-4 buyers would actually follow up, I got a bit nervous about doing that. Why tell everybody what you own,, so they can watch your house and wait for you to leave?
Now, upon first contact, I tell them I live 2 blocks from "X" landmark, so they can get an Idea if they want to travel that distance. I'll tell them the times I'm available and IF they are still interested, to email me back with a desired time to meet and I'll give them the address.

I'm currently having "buyers" problems. I'm looking for a bike for my niece (1000 miles away) on her local CL. I see a bike that seems appropriate for her, email her, she emails or calls and gets NO response or voicemail. Meanwhile, while waiting for the seller to get back, another "decent" prospect is posted and sold within a short time, because she's waiting. Voicemail doesn't get returned either, but the bike is still posted!

Answer to first question: Having someone send you a response in an e-mail is as close to a "Flake Filter" as you can find. I NEVER talk to the flake who's sitting in front of the computer, sees a bike that's interesting and wants to find out if he can get it for next to nothing or get me to hold it until he's ready to buy, because the flake doesn't have my phone number! Now they have to write an e-mail. I get to read ALL the e-mails. When I have 8 to 10 responses in one day and I read "Will you take $70" for a $100 bike or "I'd like to buy your bike next week", I don't get upset, I don't have to have a conversation with this person, I have zero aggravation, I just close the e-mail. I just move on to the e-mail that says "If your bike is the right size, I'd like to buy it tonight, my phone number is XXX-XXXX. Additionally, I never get irate phone calls when someone thought they deserved to get the bike, because they don't have my phone number and the don't know my address. I did get one e-mail asking why I didn't respond to their e-mail. So I sent them a response from my junk mail box telling them it's sold.
You may hand out your phone number, that's up to you, but my advice to other's is don't.

Answer to your second question: IMHO, I agree with your statement. Once in a while I find someone who is very knowledgeable about bikes, but it's rare. Actually, the knowledgeable ones are the easiest to deal with.

Put something like: "First come, first served" in the ad.

We must have been typing at the same time. Your experience is ridiculous - I hope that seller isn't a carpenter.

I went to pick a bike up last weekend. Spoke with the seller on the phone, gave me directions, and I said I'm on my way.

I pull up 30 minutes later, and he says "Sorry, I sold it 10 minutes ago".

When I am really interested in a bike, I respond with "I'm interested, I have cash and I will come over at your convenience".

That usually gets some attention from the seller.