There's a whole lot more to it than I'm putting into this post.

The whole online D/s relationship is based on the word and trust of another.
There are ways to ensure performance, webcam, vids etc. but if you have to have that component then to me it is lack of trust of words. With out that ... Why bother?

I have found online relationships to be difficult at best if one does not assume it crosses over into real life and is not merely an online game.
Does the Dom think and involve himself when he is not online?
Will there be or not be any real life contact to enhance the "online" part of the relationship.
How dedicated are both participants?
Do they have the time to give to it so both can have their needs met.
Yes, I said both. - If both are not having needs met where is the drive to continue it and have quality?
The two participants must have a dedication to the role that they are in.
The Dom should do follow thru and aftercare even if online.
* looks around at some*
The sub should not just write off tasks as well it is just online and they really would rather do x, y , or z.

I've even gone so far as to wonder would I have another online sub again.
The answer is yes ... but she will have to be a sub ... not just say it.

Those who live it.. know it.. and the online relationship is no less .
It is what you make of it.
Just be sure both wish to make the same thing of it.