The main difference is agent fee in KL is charged to only Seller, but in Penang, both Seller and Buyer have to pay agent fee

It is illegal to charge the purchaser for the agent fees. Probably a complaint should be made against the said agent.

Why is it illegal? This has been the practice for all property agent in Penang (and Johor as well if I'm not mistaken). In KL, the seller probably already factor in the agent fee into the property price. As buyer, if you are paying agent fee, just make sure you utilize the agent kao kao to do all the work for you (check strata title, property history...etc)

Having bought property in both KL and Penang, this is what I understand:
The Board of Valuers, Appraisers & Estate Agents Malaysia does have a regulation that mentioned an agent can only collect commission from either seller or buyer, but not both.
This is where the loophole comes in, agent in Penang usually co-broke, which means one will represent the seller, and the other will represent the buyer, hence the seller agent will collect his commission from the seller, while the buyer agent will collect commission from the buyer. Which is why from my own experience when viewing properties in Penang, most of the time there will be two different agent present.
In KL, since buyer normally don't pay agent commission, KL agent usually do not co-broke, otherwise he will have to take a cut from his own commission to pay the other agent, or he will charge a higher commission to the seller, and the seller will set their selling price a bit higher, in the end, it's all the same to the buyer.
Above are just my own observation (I'm not an agent), hopefully some agent can share some light on this.