I am wondering about the odd turn of phrase used here:
"One good sale today: £220 for two early beautiful leather-bound editions of Lewis Carroll's Through the Looking Glass and What Alice Found There and Alice's Adventures in Wonderland. They weren't the more valuable first editions, but they certainly weren't cold on their heels."
Confessions of a Bookseller (2019) By Shaun Bythell
I assume it is derived from to cool one's heels, but I just can't grok its meaning in this context and can't find its usage elsewhere.