changing tyres and battery after buying motorbike or quad is pretty standard for me.... still much less than 4,000 $ for new one.
Unfortunately, there are those on here that are that stupid, and that was not my intent to insult you. $700 is a way low price-point for a quad, even used. That price makes sense for a bike, and possibly for a smaller quad intended for kids. But if it's 250cc or higher, I'd run fast and far away. I saw one once where they guy came down from $45000 to $25000RD. The tires were bald and mostly flat, the battery was dead, and it had been sitting in his garage for months on end. Because the battery was dead, we couldn't even start it to hear how it ran. Though hopefully he dumped the gas before storing it, who knows. ottom line, $700 US is too little money to spend on something that should be safe to ride, either on trails or the street.