DVD compatibility

I have my store http://stores.ebay.com/BestDealsPoint about 3 years ago and I am selling DVD and CD.
All my items are European version (I am located in Greece-Europe).
After a few time I found that unfortunately many overseas customers do not read item description and they found (after shipping) that this item is unusable in their equipment.
Please note that European versions are Region 2 PAL discs and are incompatible in most USA/Canada dvd players.
Of course I have many customers from USA/Canada but they have multiregion/multisystem dvd-player or they watch movies in their PC/laptop dvd player.

dvd regions(0.1.2.3.4.5.6) and tv system (PAL or NTSC) are two different thinks.
Of course region 0 (Free) dvd disc plays in any dvd-player but some dvd player-tv set can't convert PAL format to NTSC format.
Many chap region free dvd-players are multiregion/multisystem but you must check yours.

I am watching all dvds in my laptop with a freeware program MPCSTAR (http://www.mpcstar.com).
It is a very good program and you can watch all dvds worldwide.