The best time to make any purchase is when it fits your needs and budget. In terms of selection though it’s usually best to purchase during winter or early spring. A large percentage of lifts are sold by companies that also rent them. While warmer climates have less variation on average winter and early spring are the slowest months. While this may or may not improve pricing it certainly improves selection. While it’s always possible to make a purchase based on pictures and videos the preferred option for most buyers would be to look at multiple options in person. This is usually difficult to impossible to do during the busy rental season.
The difference between busy and slow season is most pronounced at companies whose focus is primarily rental as they tend to prioritize that over sales when its the busy season. The same seller that seemed accommodating for a sale in January can be less so come May. Other companies who business is split more evenly between sales and rental try to be more flexible to sales in the busy season.