The Yamaha's are a great product. No, they aren't the best-built boats out there, but overall for the price, they are good. It is now "boat show season' and Yamaha may have some good incentives toward a new one that you can't get on a used. I personally have purchased two new Yamaha's (a 2009 in 2012 and a 2017 in 2017) and both have been dependable all around boats. Do they do any one particular thing exceptionally well, no, but they are great if you want to cruise, lounge at the cove, or even pull someone on a tube/board.
Since my boat spends most of the summer in Lake Tahoe and the nearest dealer from there is 100 miles and down a 7,000 foot pass, I typically don't have service things done during the season. In stead I keep a list and check it in for warranty work at the end of the season. Most of the items on my list are small...a trim question here, a leaky ballast bag, etc. Things I lived through during the season, but are now fixed.
As for buying used, if there's a good used one nearby...go for it. these boats are mechanically simple and there's tons of help here on the forum to help you out with any question that may arise.