I like your simple definition too. As a marketer, let me try and answer your question to my knowledge. It's not a science and every marketer would have what they prefer.
1.Why do many Kenyan companies market only when they need customers? Marketing ought to be an ongoing process if anyone is keen on building a brand for themselves.
Most companies in Kenya have a marketing budget which the marketers in the company direct to above-the-line. This is expensive and most budgets can't sustain 12 months so they go to media experts who advise them on how to spread (mostly around December).
2. Can aggressive marketing become a nuisance.
I find it so at times esp if the method used is boring.
Unfortunately, a nuisance is not considered to be bad, it's better than no presence at all. Sadly, due to 'limited budgets' most companies produce one set of communication and re-use it over and over. They forget that the customer is not an idiot.
3. Which marketing strategy is most effective in AFRICA?
To get people to talk about your brand positively is the best strategy be it through PR, advertising, sales reps etc.
But if you are asking about advertising strategy then tv, newsprint, magazines and direct mailers would be the best.
4. Do products sell because of Marketing or Brand?
Some products will move despite the brand because of demand, price, place, promotion. When you go to the supermarket, there are many brand names selling eggs but you'll choose the cheapest. You are likely to sell more Tuskers during a Tusker only promo as some will temporarily relocate from Keroche, Castle and other EABL products.
That said, a brand is the best way of selling anything you hope to get repeat customers on.
5. Does Marketing build a Brand or does a Brand make Marketing easier?
Marketing always builds the brand to make it easy to market. A brand in simple terms is 'the promise'.
BBI will solve it :)