Is this a "fixed week" timeshare? If it is, what happens if you can't go on vacation that week? 

Is the ownership tied to a specific unit or just the location you buy into? 

How much are the annual maintenance fees? How are they billed? Are there extra charges for memberships associated with the timeshare (exchange programs)? 

Is there a separate fee for housekeeping services or is it included in the maintenance fee?

If you are buying points based timeshare, how many points do you get for your money?

How many points are needed to book your favorite locations?

What is your booking window if you don't have a fixed timeshare? For example, a 180 day booking window means you can attempt to book your favorite resort up to 180 days in advance of your desired vacation.

What happens if your favorite destination is booked and there is nothing available for your use?

Does the timeshare go to your heirs after your death? Does your estate (or heirs) have to pay the maintenance fees if they don't want the timeshare?

What are the advantages of owning a timeshare versus booking a stay in a resort or hotel?

What happens if you only want to spend 5 nights at your resort (instead of the typical 7)?

Can friends or relatives use your timeshare if you are not able to do so?

Can you afford to take an annual vacation to your timeshare location? (Add up mortgage payments on the timeshare, maintenance fees, travel costs, and incidentals).

How does the nightly cost of the timeshare compare to the nightly cost of a rental (not owned)?

Will the timeshare appreciate in value? (Hint, the answer begins with the letter "N").

How easy is it to sell my timeshare if I change my mind 3 years after buying it? (Hint, not easy).

If attending a timeshare presentation, ask if you can record the presentation and any discussions with the sales agents on your phone.