Villian has shown his willingness to call down 2nd pair before. Thin vbet or pure spew?

$0.5/$1 No Limit Holdem
8 players
Converted at weaktight.com

Stacks:
UTG ($106.50)
UTG+1 ($100.00)
MP1 ($19.00)
Hero ($100.00)
CO ($20.00)
BTN ($152.70)
SB ($16.00)
BB ($118.47)

Pre-flop: ($1.5, 8 players) Hero is MP2
3 folds, Hero raises to $4, 3 folds, BB calls $3

Flop: ($8.5, 2 players)
BB checks, Hero bets $7, BB calls $7

Turn: ($22.5, 2 players)
BB checks, Hero bets $14, BB calls $14

River: ($50.5, 2 players)
BB checks, [color=#cc0000]Hero bets $31.5