Short answer — for most shoppers Amazon.sg offers the most consistently reliable, buyer‑friendly return framework overall; for fashion Zalora is the most reliable; for big‑ticket electronics/furniture Courts is also very straightforward. (Marketplace platforms Shopee and Lazada can be good too but reliability depends more on whether the seller is an “official”/mall/fulfilled-by listing.) (sellercentral.amazon.sg)

Why I say that (quick comparison and sources)

• Amazon.sg — centralized returns, an A-to-z style guarantee and clear 30‑day windows for many categories; Amazon has been tightening international / seller return rules to protect buyers, so refunds/return resolutions are handled consistently even when third‑party sellers are involved. (sellercentral.amazon.sg)
• Zalora — clear 30‑day return/exchange policy for eligible fashion items and a dedicated returns process (brands/exception list applies), so clothing/shoes buyers usually find returns simple and predictable. (zalora.sg)
• Courts — advertises a 30‑day “hassle‑free” returns/exchange window for many store purchases (helpful for appliances, furniture and big ticket items). (courts.com.sg)
• Shopee & Lazada — both have improved protections (Shopee’s 15‑day free change‑of‑mind/returns and commitments to rapid case resolution; Lazada’s Mall/LazMall listings and seller protections), but because they are marketplaces the experience depends on the seller (official store vs marketplace/dropship seller). Use Mall/official‑store filters for better reliability. (malaymail.com)
• Challenger — has a more conservative returns window for many electronics (typically 7 days for exchanges/returns on a lot of tech categories), so check eligibility carefully if you buy from them. (support.challenger.sg)

Practical tips to get the most reliable outcome

• Buy from “official store”, Mall, or Fulfilled‑by‑(platform) listings whenever possible — fewer seller disputes. (lazada.sg)
• Keep original packaging, tags, receipts and take timestamped photos on arrival (platforms often require photo proof). (zalora.sg)
• Start the return in‑app ASAP (within the stated return window) and keep all chat/email threads as evidence. (help.shopee.com.my)
• For high‑value items, prefer retailers with physical stores (Courts, Challenger) so you can return/exchange in person if needed. (courts.com.sg)

If you want, I can:

• pick the single best option for a specific product type (electronics, fashion, cosmetics, shoes), or
• check the current return page for a particular store or product and link the exact return window/steps.