Playing overcards

Betting with overcards not a good idea?

PokerStars No-Limit Hold'em, $0.02 BB (9 handed) converter

UTG ($2.30)
UTG+1 ($1.69)
MP1 ($0.96)
MP2 ($3.26)
MP3 ($4.40)
CO ($4.99)
Button ($1.39)
Hero ($2.36)
BB ($4.92)

Preflop: Hero is SB with K:diamond:, A:heart:.
5 folds, CO raises to $0.06, 1 fold, Hero raises to $0.1, 1 fold, CO calls $0.04.

Flop: ($0.22) 8:club:, 9:heart:, 3:club: (2 players)
Hero bets $0.14, CO calls $0.14.

Turn: ($0.50) 7:heart: (2 players)
Hero bets $0.2, CO calls $0.20.

River: ($0.90) J:spade: (2 players)
Hero checks, CO checks.

Final Pot: $0.90

Results in white below:
Hero has Kd Ah (high card, ace).
CO has Ad 9d (one pair, nines).
Outcome: CO wins $0.90.

I do that all the time, particularly with AK. Put him on a pair/draw when he's calling you down, and check it when the turn is straighty and not an over.