Bet or check?

I think I'm getting better at 400 NL, it use to demolish me but now I'm starting to make a profit..

Just sat down at the table, no read on villain



***** Hand History for Game 2431583797 *****
$400 NL Texas Hold'em - Wednesday, July 27, 03:02:39 EDT 2005
Table Table 55341 (6 max) (No DP) (Real Money)
Seat 4 is the button
Total number of players : 6
Seat 1: gboeheim ( $171 )
Seat 2: EvilEcstasy_ ( $190 )
Seat 3: altsh01c ( $166.99 )
Seat 4: maniacdan ( $640.40 )
Seat 5: bernie19 ( $691 )
Seat 6: Dwight74 ( $645 )
bernie19 posts small blind [$2].
Dwight74 posts big blind [$4].
** Dealing down cards **
Dealt to EvilEcstasy_ [ 8s 8d ]
gboeheim folds.
EvilEcstasy_ calls [$4].
altsh01c calls [$4].
maniacdan folds.
bernie19 calls [$2].
Dwight74 checks.
** Dealing Flop ** [ 7d, 3c, 5d ]
bernie19 checks.
Dwight74 checks.
EvilEcstasy_ bets [$12].
altsh01c calls [$12].
bernie19 folds.
Dwight74 folds.
** Dealing Turn ** [ 2d ]
EvilEcstasy_ checks.
altsh01c checks.
** Dealing River ** [ Qs ]
EvilEcstasy_ ???

It looks like he busted a draw from his betting but the board is showing 3 diamonds. You got to expect him to bet on the turn if he made his flush. I would put out a reasonable bet here (like 1/3 the pot). I think he was drawing to a straight or was slowplaying a set and is now worried about the flush.

I'd make a small value bet.