Cheating is becoming a national sport, reversi has the same problem. It is becoming a rarety that you don't play against a player that either has a game on the side or is using a program linked to the flyordie site. 
nothing u can do about it. try to find the honest players that's all you can do, I can give you a list of a mile long of cheaters but it's useless.

Let cheaters cheat. The legit players will always be better than the cheaters.

I'm no expert but how is that cheating, I understand it is 'dishonorable' in a light.

If he wants to continue the game, what is wrong with that? If he passes, take advantage of it. If you truly own the territory you will keep it, correct? I see it only as a time waster or disrespect for some.

Maybe they don't see it as cheating, but they just don't see it as dead stones? Technically, you are supposed to play to the bitter end, it's just an extra rule that players can agree on something being a dead teritory. Just my opinion

911 is a very strong player - one of the strongest who plays on this site. 

If he marks stones as dead you can be pretty sure that they are dead - even if you can't see it.

If you think he's wrong either don't play him or text in the game - "I think that group is alive" and he'll kill them for you....

Instead of denouncing him here you would be better off to take it as an opportunity to learn. 

You can challenge them on the text.If they refuse to see the situation then walk away knowing you're a better player by being honest.What gratification can theese people get anyway?

I know that 911 is not one to do something like that. they're one of the strongest players here, and if 911's marked some stones as dead, then yeah, they're probably dead.
There are, however sadly, loads of other players who 

do

 do that.
also, very few people on flyordie have good sportsmanship; they can't even say 'hi,' 'good game,' or 'thanks for the game,' or escaping without resigning first. (←my little rant on manners :P)
cheaters annoy me 

a lot

 too, but in the end, all they are are just cheaters.

Yes this happened to me too but I can't actually remember who I was playing against.

It's certainly dishonourable but it's not a big problem so long as you notice. You just click "reject" and play on.

Unfortunately, those of us who are used to playing against the honourable, don't always check.  We must learn to do so.

Posting names of offenders is a good idea as a warning. 

But you don't have to refuse to play them.  

Indeed it's a bad idea to refuse to play them because there is no way to verify the truthfulness of the accusations.  It's better just to play them but to be careful.  That way if the accusation is false it doesn't hurt the person.

It's very important not to punish people who have done nothing wrong, very important to maintain the presumption of innocence!

Yes this happened to me too. It happened with a group of stones which had two internal eyes.

It's certainly dishonourable but it's not a big problem so long as you notice. You just click "reject" and play on.

Unfortunately, those of us who are used to playing against the honourable, don't always check (I got caught out).  We must learn to do so.

Posting names of offenders is a good idea, but I advise you don't have to refuse to play them.  

Indeed it's a bad idea to refuse to play them because there is no way to verify the truthfulness or otherwise of the accusations.  It's better just to play them but to be careful.  That way if the accusation is false it doesn't hurt the person.

It's very important not to punish people who have done nothing wrong, very important to maintain the presumption of innocence!  A good rule for life, as well as for the internet.

Stronger players are not necessarily the most honourable although you are right that, there is a very slight tendency in that regard.