the problem with microlights is that the designers/manufacturers have always squeezed the biggest (read heaviest) engine they can fit and still meet the rules of empty weight. The customers have then decided that the biggest engine is what they think they need.
In practice there are a fair number of aircraft about that do have some spare weight between the empty and MTOW figures. I have one myself. My Rans S6 weighs just 220 Kg empty, it is allowed to weigh 243 Kg. This gives me another 23 Kg of fuel/luggage in addition to the 15 Kg that is included in the empty weight permitted. In practice the tank cannot hold that much fuel so I can sneak a bit of luggage in as well.
By going easy on the pies I keep my weight in the 83 Kg (I am 6 ft 4!) range and my partner weighs in at less than that. This means that with a bit of careful packing we can take sufficient oil (2 stroke Rotax) and personal stuff for a touring holiday to France for 7-10 days and be just legal. By the time we come home, much of the oil is consumed and some duty free takes its place in the luggage rack.
If I was looking at buying a second hand microlight I would go along armed with an inspector and 3 sets of bathroom scales. I might take the scales along if I was looking for a new partner as well!
Rans6....