maintenance question on pressure washer

couple neighbors have offered their 1-2 year old pressure washers

what are some things to look out for in terms on maintenance performed, neglected, check out, etc.. before I buy one ?

for example, if machine is a 3800psi, 4gpm system and it has been used just a few times (less than 5) in one year, should the oil have been changed twice in that timespan? would system have corroded if it just sat in garage unused for 6-8 months? would the seals leak or something else that I'm not asking?

I would look for a quality brand ther is known commercial stuff and cheap chinese brands, but you really cant know if it was run without water or froze. Try them first. Changing oil is by hours more than time for that short a period. Good commercial stuff isnt cheaply priced.