The new car manufacturers put these incentive and financing programs on in order to increase their sales.  National ad campaigns are put into place & the dealers receive the promotion kits for the sale to begin.

Should I choose 0% financing or cash rebates?
The answer depends on the interest rates at the time, the size of the rebate, & your personal credit history.  If the interest rates are high at the time you are buying a used car, then taking the 0% rate might make more sense.  This option is also likely the best choice if you have had credit issues.  There is also the buying a used car no credit option. 

If the cash incentives to buy a used car are fairly large, then the rebate may be a good option.  However, the financing manager at the dealership is equipped to answer your questions and should advise you on what would be your best option.  You may also choose to opt out on this program altogether and negotiate your best deal.  For example, buying a used car with no down payment might be the best deal of all.

Is the 0% financing / cash rebate a good deal?
A good deal is in the eye of the beholder.  0% financing or cash rebates are really no different than inflating the price of a used car only to give it back.  In doing so, the consumer believes they've received a great deal on your used car purchase.

Manufacturers would like to get out of these programs and present their product on the showroom floor at a no hassle, gimmick free, fair price, however, they have done such a good job of convincing consumers that these programs provide a great deal & create an urgency to buy "now". This process forces the manufacturer to continue with their gimmick sales approach, at a huge cost to the industry.

0% financing / cash rebate programs DO NOT reduce the vehicles depreciation!  New vehicles suffer a very significant rate of depreciation in the first 6 to 12 months.  In fact, it is quite common for new vehicles to lose up to 50% of their purchase price the moment you drive off the lot.  You might want to check out used car financing in Winnipeg and avoid the depreciation problem.