Instead of the swap-rate, the broker applies a flat holding charge after a grace period, or a wider spread, or nothing at all on major pairs. Terms vary widely and the substitute fee can exceed ordinary swap on some pairs.
Brokers restrict these accounts because removing negative swap on high-differential pairs would otherwise create a free carry-trade. Expect exotics to be excluded or to carry the largest administration charges.
Example: a standard account pays minus $11 a night to hold a high-yield exotic short. The swap-free version charges a flat $8 per lot per night after three days, which over a two-week hold is $88 rather than $154.
Related: swap-rate, carry-trade, rollover, exotic-pairs