Can a horse that bolts be trainned not too?

SUPRISE! the draft i just bought BOLTS after the lady ured me the horse didnt, well it does and dangerously too it saw a cow and freaked out bolted right into a gallop for a block until my one rein stop kicked in. the horsse was scared and shaking. ugh the horse was apparently trained... and wasnt spooky nor did it bolt. yeah right. the way my horse acted told me a few things... 1. it was never taught to STOP/learn to stop. 2. it was tramatized at some point during the training 3. it was never trainned, it acts like it had 30 days of trainning and bam sent out into the world, the draft is 10 yrs old and i swear this horse feels so green someone messed this horse up. its very spooky and looks and stares at things to be scared of. so is it possible to take this out of them 100% ? this is a dangerous issue and this horse was not worth 2000.00 to me. so what are some tips ...I really want to give the horse back im not looking forward into breaking this habit etc... but what can I do to be safe other than the one rein stop... my horse has no ground manners and is very pushy which im working on, she dosent back in the saddle either, shes just GREEN the way i see it. has anyone had a horse that bolted in fear ? did you break it out of em and was it a permenate fix? please tell me some saftey tips. i use a snaffle when i ride, i dont want to go severe with another bit... I want to see how it goes with putting a stop on the horse but putting a stop on a horse doesnt stop it from spooking...