Possible conflicts that could prevent a firm from representing a client in b/r:
1.    Atty that is also a creditor.  Ex.  client owes atty 300k in fees.  Under 327(a), Debtor can only employ attys that do not hold or rep an interest adverse to the estate.  A creditor is someone who holds an interest that is adverse to the estate.
a.    could try to get paid b/4 you file so that you are no longer a creditor, but this could be avoided as a pref.  In any case, it needs to be in the disclosure statement.
b.    Could try to get an SI or cash retainer to secure payment of bills—this could also be avoided as a pref.  (Note that if the only concern is payment going forward, may be able to do this—won’t be avoided as a pref b/c not on account of antecedent debt.)
c.    Could write of the debt or sell the claim so that you are no longer a creditor.
2.    Atty reps the company that is going b/r and its owner. If you rep the individual in his own capacity, there is almost a presumption that you rep for benefit of equity instead of benefit of the corp—that is problem.  It is possible to get a waiver to fix this, but the court may want a waiver from the DIP, owner and all the creditors.  If you have to get out b/c of this conflict, do it early or judge may prevent you from representing either one.
3.    327(c)—the fact that you have represented a creditor of this debtor doesn’t by itself disqualify you—only disqualify if there is an actual conflict of interest.