Hoe can you tell that someone is Point Gaming by using multiple accounts?

For the most part, you can't.

Users reaching an unreasonable amount of points per week, with

high BA percentages can indicate "point gaming" though unless

you have solid proof, there's really no sure fire way of knowing.

When you've seen enough of them then you build up a "nose" for spotting them.

There was a gang of accounts in this section yesterday posting questions and then giving Best Answers to the same person (whose answers were pretty poor which is why it stood out).

If you have a gut feeling that someone is point gaining then follow some of their answers to see if they either get Best Answers from the same questioners or if they win the votes all the time. If they do then drop the Y! Answers Team an email y_answrs_team@yahoo.com with the accounts involved and a couple of links to questions where you suspect the point gaining has taken place and they will investigate it for you.

Often you can't - though the really stupid ones do something like having the same or similar usernames for "feeders" and "collector".

But as Double Trouble says, you eventually get an instinct for some of the formats. A while back there was a vogue for 'general knowledge' point gaming, where a certain style of blindingly simple general knowledge question was highly recognisable as feeder for a network of point gamers.

Or it can be just a pattern where you spot a 'walled garden' of users always answering each others' questions; or a single user regularly getting BA from questions asked by a succession of new accounts; or one always winning BA with the same unfeasibly high number of votes (e.g. always 8).

if those two accounts are never on at the same time like never ever more than likely they're point gaming