OE

Credulity, beset. For the first blank, you are looking for a trait that is unhelpful in dealing with “liars and fabulists” (fabulists are just very creative liars). Duplicity and ingenuity would be actively helpful, so the answer must be credulity (a tendence to believe people too easily). For the second blank, you are looking for a participle describing “someone,” that is, you can read it as “someone (who is) foresoken/ brooked/ beset by liars and fabulists.” It wouldn't be that bad to be forsaken (abandoned) by liars—at least they would leave you alone. Brooked (tolerated) by liars doesn't make as much sense; it is the liars that would need to be tolerated by others. But someone who is beset (surrounded) by liars would have a problem, and would not be well served by credulity.