The first step to check whether a fare has been correctly filed is to establish the fare code. If I see a fare that is wildly inconsistent with the usual price for the corresponding bucket/routing/market, then I would immediately raise a red flag. If I discover the fare on FT where others have identified it as a likely mis-price, I would treat it with great caution as a unilateral error which basically means booking will be done on the understanding the fare is erroneous and could potentially be recalled. So under these circumstances I would wait until the airline confirms it will honour the booking before committing myself to any irreversible hotel/car bookings.