If a service was done, but pricing had never entered the conversation, but the bill was paid, is this misrepresentation?
My parents (elderly and live in rural area) had been contacted door to door by asphalt company.  The asphalt company said that they had extra asphalt because their plant broke down.  They asked if they could dump it on my parents' lane (gravel).  Price had never been discussed and my parents thought it was the same deal that a neighbor had come across (asphalt company dumped and laid asphalt in neighbors shed for free).  My parents said OK, and machinery came out of nowhere to lay and smooth pavement.  The company, before they would leave my parents' property handed them the bill for 7500 dollars and wanted to be paid before leaving.  My parents paid it in full. 
Is this legal?