Usually google is your friend for searching such stuff. You can find huge amount of reviews, performance testings and places to buy.
Important factors while choosing an EA would be pips volume, max draw down, max gain percentage and period of test on live and back test as long as back test made on AT LEAST 90% tick modeling quality. If it's not, it wont be accurate results.
MQL5 is a raising market and hope soon it will create its bigger face like ebay, as this webiste going more popular in world ranking www.alexa.com/siteinfo/www.mql5.com.
Why MQL5 different here they protects both buyer and seller and before launching a products human editing is involve to check any kind of scam or virus threat. A quality doesn't comes in short time it takes time to improve.
Other markets are different and their customers are general and so far other markets don't have a system to add these kind of products as on MQL5 moderators knows about products like new added product is Panel, Indicator, Expert.
For a seller next option is only a Product Own Website but how buyers will be protected there its a question.