I quit giving blood several years ago because they started DNA testing and only offered "opt out" rather than "opt in". For all the assurance that the blood bank people gave me about keeping private data private, I know that all it takes is one court order and suddenly your very private DNA profile is shared with someone that wasn't intended to receive it.
One final note - chargebacks aren't guaranteed. They work a large percentage of the time, mainly because the cost for the vendor to research what happened is much higher than the loss that they take on the product, and they are still likely to lose. When you put together your documentation, keep a copy in case you lose the case with your credit card company and need to take legal action against Dell.
Disclaimer: "These opinions are my own, though for a small fee they be yours too." -- Dave Haynie