Rent versus buy is an arithmetic question
Take the monthly rental rate, multiply by the months you would actually have the machine on site, and compare it against purchase price plus maintenance minus what you would recover selling it in three years. The crossover is usually somewhere between 400 and 700 hours a year for mid-size machines.
Below the crossover, ownership is a hobby you are financing. Above it, renting is an expensive way to avoid a decision.
Buy the attachments with the machine
Buckets, breakers, thumbs, forks and couplers bought separately cost more than they ever do bundled into a lot. Check the coupler standard before you assume an attachment from another machine will fit — a mismatch turns a bargain into a fabrication job.
Factor transport into every bid
A mid-size excavator is a lowboy load with permits. Moving one three hundred miles can cost more than a month's rental on a smaller machine, and bidders who forget it routinely overpay by the exact amount of the freight.
Parts availability outlives the discount
An orphan brand with no dealer within four hundred miles is cheap for a reason. When the machine is down, availability is worth more than the eight thousand dollars you saved.
From the auction floor
See how this works on a real lot.
Every listing carries its inspection report, its full specification and its bid history. Read one before you decide what it is worth to you.