I never liked 'fish on TO' for precisely the same reasons as this:
However, this...
...doesn't work!
Here's a general scenario that happened to me more times than I can count:
1. I advertise on trade (wts 'adventure' ls rtf 'price' w/m).
2. Interested buyer duly whispers as requested.
3. I put fish trade up on TO for 'price'.
4. Player who hasn't whispered opens TO and buys fish intended for player who whispered.
5. Player who whispered complains they cannot find trade or that it failed.
I then have to explain to player that bought fish that I asked for whisper first and the trade was intended for someone who followed my instructions, arrange a refund, put up second trade for actual buyer and it's just a complete mess because some 'quickfire johnny' just assumes that 'fish on TO' is the only way things are done now.
I could also mention that one time I got a bunch of grief from one player because they couldn't be bothered to whisper first, who wouldn't shut up about it until I pointed out that the effort he had spent whining in the trade tab could have been used to whisper "me please" a dozen times over.... oh... wait.. I just did!
In the end, I just gave up because one lonely fish doesn't stand a chance against a flippin' tidal wave!