Can trading system determine / infer a Mon's level?

I think the easiest way to determine level based off the trade estimate would be to look at the highest value, though it would be a little cumbersome. You would need to know a Pokemon's maximum potential CP at any given level before going into the trade.

Say you trade a Magikarp and the CP range tops out at 125. A 100% Magikarp reaches 125CP at level 20, so you would know there. This becomes cumbersome because you would need to know the maximum CP for every Pokemon at any given level to determine it based off the trade preview.

An easier way would be to use an IV checker that examines the white curve indicating how powered up the Pokemon is. I use GoIV and it uses the CP, HP, appraisals, whether it was obtained via raid/egg/research or not, and the power up curve to determine exact level and range of potential IV values. Some IV checkers need to be updated for lucky Pokemon, so keep that in mind.

An app could do it easily by reading the upper range which corresponds to 100% IVs, but an app can just as easily read the level arc. The trade lets you determine the level without reading the screen or a screenshot, but it's way too much effort to use with any frequency.

(By the way your Carvanha is level 33 or 34. Level 35 shows 8000 dust for powerup.)

Still room for a half level error. The level of a pokemon is lowered to the nearest whole number when traded.
https://www.reddit.com/r/TheSilphRoad/comments/93gg7u/trading_can_lower_the_lvl_of_the_pokémon/

Just use CalcyIV on Android, or Poke Genie on iPhone.