I tell them to salvage because the mods won't reach the climax of their value through a sale. In many cases the buyer does not want the mods on the item and will mod it to their liking and will not pay any extra for the attached mods.
In any case, the above user could simply salvage with a perfect salvage kit and sell the said mods ~20k for all 3 at the expense of ~1.2k for the kit.
This of course is only done with mods that retain some value, I would not advise people to salvage any worthless mod out there, only ones that retain some value and where the mod will not reach the climax of this value through a sale.