Earning silver isn't too difficult though and isn't that different than gathering feeders. The easiest way is to farm the early missions and operations for normal cards which you will sell for a little over 200 silver each. If you gain about 3000 silver per 60 energy selling cards this accounts for about 20-30k a day if you check every hour or two. Now, when you're enhancing powerful cards, you know that 20-30k doesn't come close to being enough. That's why you need to stack this with other methods.
*Thx to Joel for pointing out if you want pure silver, Operation 3-5 offers more silver if you sell all the cards. Since I am normally gathering feeders as well, I prefer operation 2*
Selling Rares: Do not sell rares to vendors. If you have new players in your team or alliance list, you can sell Rares for a lot more than the 12k that the game offers. A lot of players will pay a lot more silver than that for a rare.
Events: A big key to gathering silver comes from minimizing costs of things. Silver in Marvel WoH is given out in heavy amounts during events, normally at the end of one you can have a pretty significant stockpile. When you participate in an event, participate heavy and understand that the silver won't last forever, so don't just spend it all willy nilly.
|Vibranium, event card worth 10k silver|
Selling Boosters: Sometimes players in your alliance have a lot of silver but want to boost a card quickly. During this time you can gather and fuse cards to their final form and sell them to any alliance members needing them. They get cards fast rather than waiting for their energy to replenish or using energy packs, and you get silver. Works out for everybody.
Hopefully this helps some people having silver issues.