▁valu ation ▁and ▁generally ▁accepted ▁trad ing ▁norm s ▁do ▁not ▁rule ▁the ▁terms ▁of ▁trade ▁for ▁products ; ▁in ▁this ▁case , ▁there ▁is ▁no ▁cons ensus ▁on ▁what ▁products ▁are ▁worth , ▁or ▁it ▁is ▁unknown , ▁and ▁products ▁will ▁trade ▁on ▁all ▁kinds ▁of ▁different ▁terms ▁which ▁could ▁vary ▁greatly . ▁Struct ural ▁une qual ▁exchange ▁– ▁alternative ▁or ▁compet ing ▁sources ▁of ▁supply ▁or ▁demand ▁are ▁absent ▁or ▁blocked , ▁dist ort ing ▁trad ing ▁r ati os ▁in ▁favour ▁of ▁those ▁in ▁a ▁stronger ▁market ▁( or ▁b arg aining ) ▁position . ▁In ▁that ▁case , ▁the ▁true ▁value ▁or ▁cost ▁of ▁products ▁may ▁devi ate ▁greatly ▁from ▁actual ▁s elling ▁prices ▁for ▁a ▁prolong ed ▁time . ▁Other ▁restrictions ▁on ▁trade ▁and ▁what ▁people ▁may ▁do ▁with ▁resources ▁( legal , ▁technical , ▁protection ism ▁etc .). ▁Tax ation ▁and ▁subs id ies ▁to ▁produ cers ▁by ▁government ▁( sub s id ies ▁less ▁indirect ▁tax es ▁paid ▁can ▁be ▁a ▁significant ▁addition ▁to ▁the ▁value ▁of ▁gross ▁product ). ▁Dis par ities ▁in ▁currency ▁exchange ▁rates . ▁Mon opol y ▁pr icing ▁where ▁fir ms ▁drive ▁up ▁prices ▁because ▁they ▁control ▁the ▁supply ▁of ▁most ▁of ▁the ▁market ▁demand ▁( per haps ▁because ▁they ▁own ▁br ands ▁or ▁pat ents ), ▁or ▁tempor arily ▁lower ▁prices ▁to ▁increase ▁market ▁share . ▁Lar ge - scale ▁spec ulation ▁driving ▁up ▁prices . ▁Admin ister ed ▁prices ▁set ▁by ▁a ▁state ▁authority ▁or ▁a ▁mon opol ist