Hello!
Almost all of the veteran players know that ditto is currently useless outside of getting your bike. Unfortunately, a lot of the newer players do not know this, which leads to a lot of veteran players being in a position to scam these new players under the veil of "helping them".
To prevent this from occurring, my suggestion is to make it so Ditto CANNOT be traded. There is no value to having a ditto and there is no need to trade a Ditto, unless you are a malicious person who wants to scam a "newbie". And anyone who says that they are selling "for dex completion" is a liar that wants to take advantage of a newbie.
I'm semi-familiar with coding and I do think that this is a simple enough solution that can be implemented into the game (but I'm not familiar with the code, so I can't say for sure).
What do you all think?