This advice is for buying for personal use, not a rental business.
Suppose you are considering acquiring a week at good ol' Mugwump Swamp. You love it there, your family loves it there, you go every year. You've been able to rent that same unit pretty reliably, and you typically pay $2,000 for the week. You find someone who owns a week/unit that works for your annual trip. The current owner is offering to transfer it to you for free. Fees are a steal, only $1,800 a week! Seems like a great deal! You're saving $200 every single year!
In the words of Lee Corso,
not so fast, my friend. You are obligated to stay there (or to rent it to someone else) every single year, good times and bad. If the week goes to waste only once every ten years, you will end up paying the same money to just rent it when you wanted it than you would have owning it. What's more, being an owner means that's where you are going most years, even if you get a little tired of it, want to take a break, whatever. If you are a renter, and you want to take a break, you just do.
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I will admit that I am intentionally painting one of the best benefits of being a timeshare owner as a drawback. That benefit is: owning is a use-it-or-lose-it proposition. Being a timeshare owner means you are much more likely to actually take a vacation, because you've already paid for (part of) it. I can gaurantee you that owning timeshares has not saved me money vs. what I would spend on vacations if I was not an owner. But, that's because I
take more vacations, in more places, more often. These aren't things I can't afford, but if left to my own devices I might not have done them. It's another example of
paying yourself first.