Sandbagging?

How to play against such a player?
He's over 2000 in Puzzles, over 1650 in Rapid, 1420 in Blitz, and playing as a 700 in Bullet.
That's sandbagging in my book. Definitely not fair matchmaking.
Just frustrating. 

Jaesperr, he's played 4000+ wins and 4000+ losses in Bullet. Pretty evenly spaced. 
Otherwise I would agree with you, but with that many games, I thought it suspicious.

Most players play better moves at longer time controls--more time to think. Perhaps this person doesn't have good chess "instinct" and his first idea (which you play in Bullet or lose on time) is bad more often. When my chess club had a blitz tournament every two months I always lost most of my games, but against the same opponents in classical I was rated 2100 and won regularly.

700 points difference between blitz and bullet don't seem to be too crazy. I am 500 lower rated in ultra bullet than in bullet. Maybe he/she is just slow.