I actually would like to share my experience with hunting for a diamond engagement ring.
#1 - Went down to Jannpaul, good service was my first impression, was amazed at the new knowledge gained. Eyed a 0.4 stone ring for around $4,000k SGD
#2 - Went down to Love N Co, service was okok, but very secretive with their diamond GIA specs, cant bring copies home. Then was given conflicting information about HCA score, where the salesperson used HCA score to prove a point that their diamond is good, and end the pitch with "HCA is an outdated system"
#3 - I knew there was more, so i did research on online retailers, HCA scoring and diamond dimentions. I also learned from diamond forums (pricescope.com etc) where members discussed how to find great deals.
#4 - Found out that while local jewelers such as jannpaul give good service and introduction to diamonds, their teachings were biased towards you paying a significant amount of price difference for an insignificant (to the naked eye) increase in quality, always pushing their cuts/color/clarity at the expense of carat size. Also at jannpaul, want to reduce the cost of these stones ? Ok allow me to find you a diamond with strong fluoroscence! (YUCK!)
#5 - Went to James Allen, which is highly reputable online jeweler and praised for it's service. The thing about James Allen, is that all their stones have 3D imaging.
The key is to go down on color and clarity, while finding an "EYE CLEAN" diamond, that has a HCA Score close to 1.0. My eye caught this SI2 Diamond (which jannpaul frowns at when you ask about it), that actually looks more like a VVS ! :
https://www.jamesallen.com/loose-diamonds/round-cut/0.70-carat-g-color-si2-clarity-excellent-cut-sku-1963743
Here is the GIA Cert :
#6 - Besides having an awesome HCA score of 1.1, excellent in all four categories and absolutely
NO FLUOROSCENCE 
, as you can see on the far left, a very small inclusion that is almost an invisible cloud. Requested Idealoscope and ASET, but only received Idealoscope, great service and response so far ! Here is Idealoscope of the stone :
#7 - Selected a setting, and the order was underway. Received the ring in like 2-3 weeks, and was amazed. The packaging was superb, lifetime resizing and maintenance service. The stone really exceeded my expectations. For $4k i had almost doubled my carat size by cleverly dialing down on clarity and color but carefully picking an "eye clean" stone, if I were to get a similar stone from Jannpaul, I wouldnt be surprised to pay upwards of 7-8k. People I know whom bought locally paid around 3-4k for a carat size of only 0.3-0.4, feel bad for em
TLDR : My experience is that Singapore jewelers leverage on your lack of knowledge of diamonds. Though the learning curve is steep, spend weeks to educate yourself and you will reap huge value through your newfound knowledge and with your lady having the biggest stone without sacrificing quality or bling. A proposal ring was my most expensive single purchase of my life thus far (probably yours too), it is not a small amount of money, so be very critical.
Happy to ans any questions