I created a regular trading offer in the market (not limited by "only guild" or the like)
I sent that trading offer to a player on my friends list (not a guild mate) via the message system.
That player was not allowed to accept the offer via the message dialogue. He got a message like "you are not a guild mate". The trade offer accept button on my side was greyed out (my offer) but also had an icon comprising a hammer (I think) and a shield. There was no indication in the market that said offer was "guild only". The other player could accept the offer via the market.
Version: Browser, Flash 1.141.5b3f95f3af1 (on de20 live server, I cannot test this on beta anymore, since I gave up my city here)
I sent that trading offer to a player on my friends list (not a guild mate) via the message system.
That player was not allowed to accept the offer via the message dialogue. He got a message like "you are not a guild mate". The trade offer accept button on my side was greyed out (my offer) but also had an icon comprising a hammer (I think) and a shield. There was no indication in the market that said offer was "guild only". The other player could accept the offer via the market.
Version: Browser, Flash 1.141.5b3f95f3af1 (on de20 live server, I cannot test this on beta anymore, since I gave up my city here)