I've done a few as commissions over the years, but only when asked. I've seen a number of pretty mediocre models on e-bay for fairly high prices - certainly not to the quality to command the price asked.
The problem is, to research, build and finish a model to any standard takes time - lots of time in the case of a high quality model. Research alone can take hours, spread over months, even years. Now, given that this is done as a 'job', and charged per hour of work (not counting research), then it can be seen that, to recoup the hours spent, let alone materials and the kit itself, even at a 'minimum wage', would amount to a substantial amount.
My average 'fighter size' build takes roughly between 80 and 120 hours, so even at a measly £5 per hour (approx $7.5 per hour), that works out at a basic cost, not counting materials, or profit, of between £400 and £600 ($600 and $900) !!
Now we see the problem - unless someone really, really wants that model, and its is of the very highest standard, it is not going to sell at that price!
It's a similar situation with paintings. If I paint a picture, or build a model to commission, it is to an agreed and reasonable price, way below anything shown above. If a painting (or model) is sold, perhaps because some one saw it and wanted it, then there is a little more leeway for pricing, slightly higher, but not too high!
Potential purchasers, and lets say there are a number, for a number of models, perhaps one per person, will more than likely baulk at a 1/48th scale P-51, for example, nicely presented on a detailed base, if it's priced at £400 (even if the standard, and the amount of work, warrants that price).
But, the same model, at, say £75 ($110), might be a different story.
This means you may have some chance of selling a few models at a much lower price, but not much chance of selling any models at a higher price.
Then, of course, given the model has been sold, there's the problem of packing and shipping it (with the costs involved) without damage .....