[Van down by the river]

Price is usually and indicator. Wild caught are usually cheaper. Sometimes if they are locally bred the price is the same or close.

How do you tell if the fish are captive bred or wild caught?

There is no difference. They are the same fish, sometimes captive bred will be smaller only because they may reach the store at an earlier age. Sometimes captive bred haven't developed their stripes fully.

In the beginning captive bred were paler colored and had some issues with disease resistance; but not anymore. Better breeding,care and feeding methods have dramatically improved over the years. Now we will start to see color strains, and domestication from the commercial breeders.

If you see a tank of like 30-40 (or more) small A. ocellaris, it's a reasonable assumption that they're tank bred

True.
Generally they will be fairly uniform in size, but again not always as runts, and bolder feeders from the same hatch will be different sizes.

Is there a chance they'd show you the waybill?

Forget asking for the waybill, it is not an appropriate question to ask a store owner, REGARDLESS of what some Canreef hobbyists think.
It is the RARE exception that it will be shown and is no indication of the quality or practises of the store. (If anyone feels like wasting allot of time you can search for the previous thread on this)
-Not an attack on you teevee . This was previously a very "hot" debate.

well, the thing is. I can't really trust their word! they seem a bit..shady.....i am sure they'll say anything to sell their fish....they'll just tell me what they think i wanna hear

If you feel you can't trust them why do you buy from them?.....
Use your best judgement and the judgement of other experienced aquarists you do trust.

If you see a "mated pair" i.e., one obvious female, one obvious male (females are larger than males), well ... it takes time for them to pair up... so .. unless they were traded in or something, it seems odd that something like that would come from a breeder.

"Mated pairs" usually don't come from breeders. Why would they give up good broodstock? They are usually wild caught. Taken from the anemone and shipped together. Do I think sometimes they just put a small clown with a big one? Sure, but we will never know the difference.
They come from the exporter in bags that are taped together so the pair remains together.

I'd really like to discourage people from buying these pairs as the removal of productive breeding pairs from the reef seems counter productive to the long term of the hobby. With the removal of two fish we have lost the hundreds of larva and juvenile clowns they produce every month. Also the adults would be more able (than juveniles) to protect the host anemone from predators. Juveniles from the wild will have a lesser impact. Ideally wild caught would be only used for genetic diversity for breeders and all hobbyists would purchase captive bred.

Young clownfish grow quickly and if you don't have the patience to wait for them to pair and mate, then you most likely don't have the patience to raise their young anyways.