@ the OP, well, yeah, as you can see those "perfect" mods really aren't what everyone wants.
As for how to deal with it in trade, get sets of +30 and 20/20 mods for the martial weapons you're trying to sell (they can all be had pretty cheap these days, shop around.) Don't add them to the weapons. When you have a potential buyer for your weapon, offer it in trade. If they like it, cool. If they cry noob because it's not "perfect," change your offer to include the 2 appropriate mods. Tell them the price has gone up 50k-100k to cover perfection.
Realize that your trouble with selling may not actually be the lack of "perfect" mods. I can think of two other explanations. One, the potential buyer you've met is a power trader trying to get you to sell the item cheap and increase their own profit margin. Two, the item you're trying to sell really isn't worth all that much due to a not-so-rare skin or a >9 requirement. Don't put too much faith in the Guru PC stickies. At best, they were guidelines. I usually find them way off the mark these days though.
I disagree about sundering and fortitude being rare mods these days. Perhaps there was a time when that was the case, but no longer. I find as many of those as I do of other mods now. High demand, not low supply, is what keeps their prices up now.
Since everyone else is hopping on the how much I love/hate sundering, I can too. Me? I hate sundering. It's preferential to martial weapons! I refuse to play until ANet implements sundering staff heads and wand wrappings. My casters need more wandage DPS!
Thanks in advance to anyone that replies to that thinking I'm serious. It'll make me smile.
Cheers,
Luny