A timeshare is not an investment. Investments are designed to appreciate in value, generate income, or do both. A timeshare is unlikely to do either, despite what the salesperson says. Thus, selling for a profit is an uphill battle considering you need to convince someone to pay more for a used unit and factor in all the fees you paid over the years.
The huge volume of used timeshares on the market, the appeal of buying new versus used, and the marketing muscle of the firms selling new timeshares all work against the idea that you will make a profit reselling your used timeshare.
A timeshare is not an investment, it's a vacation. It's also an asset that is likely to lose value over time. Ultimately, timeshares are like swimming pools, if you buy one, do so because you love the idea of owning it, not because you expect to make a profit.
If you do take the plunge, remember that you are buying a repeatable vacation. Just as spending $2,000 on a trip to an exotic beach is not an investment; neither is spending $50,000 plus maintenance fees on a timeshare.
The very nature of the sales process should be a hint about the reality of the issue and the hard sales techniques used by the sales people. Have you ever heard of a mutual fund, purchasing a house, or any other investment that offered you a free weekend in an exotic spot just for giving the product a try?
Like any major purchase, the decision to buy into a timeshare is a decision that requires careful consideration. It involves a large amount of money up front and considerable recurring costs. You should ask plenty of questions, be aware that you should know that the value of these timeshares is in their use as vacation destinations, not as investments.