Chances of getting caught completely depend on how thorough you are in your work. I have heard of hundreds of people getting caught in SE'ing, and 99% of them was because of their lack of cleanliness and clean-up when doing the procedure. You can take them from shops, but I suggest to use craigslist or ebay to obtain the Serial number from the sellers.
A drop is a house that you use as a substitute for yours to obtain a product anonymously. So SE'ing a computer and getting it sent to that house instead of mine so that if I get caught the authorities will investigate the wrong house.
If you need ANY advice, hit me up. I've had 6 years of experience in SE'ing, and I can help you get anything you want. If you need my methods however, a charge will incur
PM me if you need anything else.