>>34098085The only time May shouldn't have trusted him is the first Kanto contest:
1. When Harley first met her, she never knew him, so of course she was surprised when he tricked her.
2. In the Hoenn Grand Festival she was willing to give him the benefit of the doubt since he said he was sorry and was pretending to be remorseful about what he did. So I can see why May went along with it. Likewise when her Skitty was messing up she fixed it herself on stage.
3. In the first Kanto Contest, Harley was helping Nurse Joy with injured pokemon, and Ash and Brock believed him too. However this time May started to distrust him.
Then in Harley's remaining appearances he never tried to trick her anymore and just acted nasty upfront.