If you look at a EA or a indicators for sale it will show you how many demo downloads and how many activations. It displays something like this
Does Activations mean out of 5479 downloads only 5 people Activated and purchased the EA?
No. The number of downloads increases with every free demo download to the strategy tester.
5 Activations means that users can activate this product on up to 5 different computers.
That is how many times you can activate the product eg after reinstalling windows etc.
You have to find out for yourself how the product is good quality.
I can recommend to seek strategies that have a credible and who have quality backtest. And of course you gotta take into consideration Which business style you prefer