After a one incident where a painting sold immediately after I posted it and it was still wet, I stopped posting wet paintings. The customer was good about waiting for the painting to dry before shipping but I prefer to ship ASAP to keep my "to do" list streamlined and not have sold paintings hanging around.
Because of that I use a dish drying rack (wooden dowels spaced about 2 inches apart - maybe it's a CD rack) for paintings to dry on and wait until they are dry to the touch before posting. Enough that I feel I can confidently wrap them in tissue paper and bubble wrap before boxing them for shipping. That way, when (if) a painting sells, I can immediately box it up and ship it out. I'm happy to have my "to do" list clear and my customer is happy to receive their painting so quickly.
Side note: My husband made me similar drying racks to fit 6x6's and another one for 8x8's. I like the stretcher bars to hit the dowels. If you paint on panels there might not be an issue.
So that is how I now approach the timing of posting and mailing of my oil paintings! Hope this helps!