Seasonal Price Changes
A new big thing is websites which track prices on Amazon
partly of interest to third party sellers playing pricing games with competition. big business on Amazon
now. e.g. https://thetracktor.com/
Haven't checked for ebay
Get the URL of the catalog page on Amazon
to put in this engine (as no ASIN shown). Free website.
For a medium Robomow RC306 a year long or more history of both new and used prices is shown, with an apparent seasonal pattern which makes sense in marketing terms so probably not accidental.
New prices peak now starting May, for a month at the beginning of the gardening season with most demand, while used prices fall. New prices will fall end of summer in August, while used prices will then peak.
I picked this model to try and get one with some sales volume for sample data to be more representative, but you could check others and Husqvarna.