My thoughts
Gor operates on Honor and Trust; I think Honesty and Responsibility also. The slave must trust their Owner enough to give themselves into their hands. Trust that they will care for his/her life and well being as long as he/she is pleasing. A Gorean Owner takes the responsibility for the slave in what he/she does, how he/she acts, what he/she wears, what he/she learns; responsibility for all parts of them as well as their well being and health.
A true Owner does not willingly damage something valuable to her/him. There are pretenders, abusers, and people trying to do something they really do not know much about but then that happens in most lifestyles.
Goreans would say that an Owner must master themselves before they can master a slave. We do not need to prove ourselves as we are confident in whom we are.
Another big difference is I find that BDSM seems to be about sex and it seems to be the main point of BDSM. Gorean slavery is about service, of a slave giving to their Owner and of pleasing them, sex is not the most important part. Most Goreans do not seem to do much BDSM play, there may be some bondage but it is not an important part to being Gorean.
An Owner does not whip a slave for erotic pleasure but to punish him/her. To make them understand that they were found displeasing in their actions or attitudes and that they need to change what was found to be displeasing.
BDSM is not normally done by oneself but a man or a woman can be Gorean without owning a slave. Being Gorean is an attitude and a way of life, not something you do in the bedroom/playroom or when you put on special clothes to go to a play party. It does not turn on or turn off when convenient, Gor is.