I agree with what moondog says here about fakes, as it has been my experience. As for watches, I have bought about 50 for myself and friends over the past few years, and would say ~ 90% have worked accurately. Always be sure to ask for "A quality". You might not always get it, and in fact it might not actually exist, but it helps get the best watch possible. Also, the automatic watches tend to me more authentic ("A quality") than the battery ones in details, weight and quality. I have had great success with Cartiers, Brietlings, Panerais, Patek Phillipes, Franck Mullers, and Rolexes. Lady Rolexes are not as good (perhaps more difficult because of the size).

Something to try is when you see one you like, set it for 12, shake it up or wear it, and make sure that by the time you're done and ready to pay, it's been running accurately.

As for handbags, the same "A quality" rules apply. My wife has gotten many dead-on knock-offs, which when compared to the authentic ones in the Hong Kong designer shops were undetectable.

DVDs and computer software has been less reliable. New releases are definitely inconsistent quality, and all others are hit or miss. Good news is that for ~$1 USD, you can also afford to throw them out if they don't work. Computer software often lacks the SN required to make it work, or just results in a quirky installation. Again, it's so cheap that it's worth trying, but beware that it might not work or install properly.