I've been reading various forums for over 2 years now.
I also check with the "for sale" sections quite frequently. Many custom cues are sold again, even 1-3 months after they've been received.
Most of them read "I cannot get along with the cue" or "it's too expensive to be a daily player".
Recently there was one guy trying to sell a cue butt, and no matter what shaft he put on this, it was dead.
The amount of customs to be sold again is shocking.
The amount of crappy, high deflection shafts is shocking.
I cannot remotely advice anybody to order a custom.
Not even remotely.
Please continue now.
There are many other factors to consider beyond the making the assumption that because people sell cues shortly after purchase it indicates custom cues are a poor choice.
I'm sure that some sell cues for the reasons you state, but some people buy cues just to try with the plan to then sell them a few weeks later. Anyone who pays full value for a cue on the off-chance it will suit them is making a fool's purchase.
There is also the oversaturated, and shrinking, market into which more and more cues are added each year.
Other players buy cues trying to flip them for a $50 profit and when they don't sell, they are relisted into infinity until they realize cue flipping is not for them.
A cue that fails to sell in a matter of weeks or even months, might indicate it is not priced correctly, or might be a cue that needs more time to find the correct buyer.