how many times is a model sold on average?

More like once per year.
Some models never get a sale.

it really depends on the models you are selling, some models sell often, some simply do not sell at all.
it is also very hard to predict what model will do good, and what model will do terrible.

on average though, i would say that models get sold a few times a year, at most. (again, some will do better, other worse)

this also depends on price, quality and on category, but the sales that you are mentioning, ones a week or ones a month, are way to optimistic.

I am agree with trimitek - one model may be sold twice, another may sold never...

I agree that it depends 100% on the type of model you are selling, the quality of your work, the quality of the preview renders and the price.

This is why it is very important to build a large portfolio of models, without sacrificing quality, so you can see for yourself what has the potential to become a good selling product and build around that category. If you are very lucky, you might model something so good and so interesting that you find a lot of people purchase it often, but that is not the norm.

I have some models which get purchased at least once every week, I have some which get sold maybe once a month, and then I have some which have been up for years but just haven't had any interest at all. Obviously, the models which haven't sold even 1 copy in years are usually the types of models I just don't bother creating anymore. So it's a business where you need time and patience as well as talent, and a little bit of luck.

You need to get very creative, for example i have model that is sold 52 times in a year (model don't cost 5$) simply because there is no other model in that particular category so there is no competition at all (take into account that i don't focus on selling models via profile). Finding, let say interesting stuff to model without or with small competition is tricky but very profitable from my exprience. If you want to do a model that's already have 20 results when searched, you need to do something that will made your model stood out, and this in my expirience is quality only. Than you have other things like presentation quality, sensible pricing etc. Competition is a big thing around here when it comes to selling, that's why we don't like thievs so much around here.

Suppose you have a current model and you know that it has a certain demand, what you need, first of all, is for the buyer to decide that your model is the best among the options they will find.
If, in addition, your model has little competition, your possibilities increase.
They also increase your possibilities if your model offers an adjusted price for its market, always with the best quality, this is what the customer buys, quality, and will pay for it the right price without problems.
For the rest, there are models that are not sold, but that does not mean that they will never be sold, having a wide collection also increases your possibilities, you never know when someone may need it.
Some of the models that a priori thought that they would never be sold because they were too personal and far from reality, have ended up having good sales.

With these answers, I wonder if I can do any sales...oh well, I'll give it a shot.

Random, it's all random. You upload, sometimes you sell, sometimes you don't, sometimes 1 model will sell many times and sometimes they won't sell at all. Good luck!

There is no way to answer this question the only answer that is correct is more than or equal to 0 times.
Some of your models might sell more than others.
Some may sell more this year but subsequent years hardly any sales.
Other may have consistent monthly sales.
Some months you may see more sales due to holiday discounts.
Some may never sell at all.

There is a saying in advertising, "Half of the money invested in advertising is money lost, what we don't know is what half is lost."
This does not prevent companies from investing large sums in advertising and promotion, and that is because the other half does produce benefits.
Going the distance, it is the same case, any product needs a target audience, and there are techniques to reach it.
A model abandoned at random, floating in cyberspace, has little chance, much less than a model created and directed to a specific audience, and properly promoted (read, spend time or money on it)