Dumkopf!

Gosh! what a bargain...can this be true?
Unbelievable value, so versatile too!
Lest I should waver, here's cash on the nail...
Lo! and hey presto!...this gadget can't fail!
Integrity certain, for you I can trust...
Burnt fingers...ouch! can't see you for dust!
Learnt lesson? um..aa...ja well, and no fine...
Ever the sucker...first letter, each line!
!