I understand the potential duplicity with the current system, and I agree that the authenticity holes mentioned should warrant this suggestion in displaying the IDs and/or the IVs of the Pokemon in the trade. However, the trade-screen window likely won't be able to have stable textual alterations without a new client—this has been suggested before, and it was noted by an Admin that it would likely crash the client/server to display different data (IDs and/or IVs, in this suggestion) than what the client already accommodates for (the Pokemon name, level, etc...).
The best course of precaution that I can advise for now, if you are really worried about this type of scam, would be to ask them to display all of their Pokemon in the trade window, then to see if there are any equal-level duplicates of the Pokemon they proposed to you; if they send you the IVs while in the Union Room floor, then show that there is no other Pokemon of the same level (it's an off-chance that any intently honest trader would), then they won't be able to pull off this type of switcheroo without going downstairs back to the PC. This may require taking more steps than what could be readily provable in a future client update (allowing you to cross-examine the IDs/IVs of a Pokemon from the /iv command and in the trade window), but it still exists as a surefire way to negate it in the meantime, for those who prefer to exercise caution.
