To exclude anyone who has a write-off (regardless if he has another gift on his record):

1. Create a constituent query
2. Filter on: Gift Type not one of Write-Off, Matching Gift Write-Off

To exclude anyone who has a write-off unless he has another gift on his record:
1. Create a constituent query
2. Filter on: Gift Type one of [all gift types except Write-Off and MG Write-Off]