I am reviving this topic as I did not know you could sell the certificates. Don't know why I didn't realize it, but as soon it arrives whatever sim gets it out of the mailbox just keeps it in his or her inventory unless I needed a space to be filled.
I am sure that there may be others who have joined the forum don't know this either and would be glad to hear of it.
I have been searching to find out which paintings is best to sell. Not only because my sims inventories are getting quite full, but for some reason they are disappearing off the wall. I can put one up and it shows up there and as soon as I let go of it -- it vanishes and I can't find it. Some were ones that I really liked.
Anyhow, with now being on my fifth generation, keeping the heirs, spouses and offsprings have built up. Glad to know that I can clean out the certificates, which will clear out a lot of wasted space.
Anyhow, with knowing I can sell the certificates, and going ahead, unless someone suggests not to, sell all of the average paintings I can get rid of some. That should clean up my overloaded and messy inventories, I have a LOT of paintings and certificates.