I usually either post WTS: personal sales (things I own) or FS: which are at my FFL. If people have replied to the FS: posts I cannot delete them. They roll of the first page and I do not intend to bump them as I have not received many responses.

Since I cannot delete them does this mean I cannot post a personal WTS ad? If I have another WTS: ad that is old but the item never sold and I can't delete it how old does it have to be for me to be able to post another ad.

I had an personal ad locked recently before I could post the gun was sold because I opened a FS: ad. The personal ad was not on the first page.

How do I determine when it is acceptable to open another ad?

You're allowed One active WTS ad. Period.

Only list items for sale that you own.