You've been had by that shop keeper
Beardies need a night time temperature drop otherwise they don't 'shut down' and rest properly.
You can try selling it on here... or saving it for another rep
Heat mats are useless on the wall, they don't heat the air. You're just using up electricity and gaining nothing.
A drop below 70F is fine too, it can easily drop into minus numbers where they live and they manage to survive quite well.