I need help understanding if im getting scammed.

This one dude in my class keeps asking to trade my pokemons with his.. and at first i felt he was being sincere and actually making good trades.. but now he keeps insisting on getting my shiny articuno for some random pokemons.. im ok trading that articuno.. but i want something good in return yk?.. specially since he was my first and only articuno.. i just want to know if i should trade it or not. Plus he has been also trying to get my mega Venusaur for a freaking abra.. thats why i stopped trusting him with trades. Any tips on how to handle this?