The rating of a house reflects the appreciation the owner of the house has for your design. The better you design, the higher your rating will be. A higher rating will result in a bigger gem reward as well.
Rarity affects rating
Each piece of furniture has a rating attached to it. This rating is based on the rarity of the furniture. The more rare a piece of furniture is the higher the rating is.
What about likes and dislikes?
Each house has a set of likes and dislikes. For example a house has a like for red items and a dislike for yellow items. By placing a red piece of furniture its rating will be higher because it is red. Placing a yellow piece of furniture will result in a negative rating. So be sure to look at the likes and dislikes for each house.
What is synergy?
Synergy happens when a piece of furniture has more than one like. Its rating is than boosted even more! For example a house likes the color red and likes the category art. When you place a red piece of art synergy happens. The rating of that item will have three boosts.
Repetition is discouraged
When you place one item too many times it may result in a negative rating. So be sure to check the overall rating when placing duplicates of a single item.
What about items that are liked AND dislikes?
Sometimes pieces of furniture fit both the like and dislikes of a house. This might cause your overall rating to go up or down. Be sure to check for synergy in that case. Sometimes the boost synergy gives to the rating of a piece of furniture is higher than the negative rating it gets from a dislike.
How to I earn Gems?
The rating of a house is converted into gems. This means that a higher rating will result in more gems per hour. The actual conversion rate of rating to gems may change with each update of the game.
How do I remove certain pieces of furniture?
Once you finish all the objectives in a house you are allowed to remove all pieces of furniture. Sometimes this is needed to get the best possible rating.