Was it here or perhaps Thai Visa where I read of someone complaining a Samsung Phone they bought off Lazada was giving problems and the buyer insisted it was not a new itme as he thought, but one which had been returned to Samsung, they had fixed it and it ended up for sale, cheap, as 'new' on Lazada?
Anyhow, my recent purchase from them, a new lappy battery, was fine.
Don't doubt there are some dodgy sellers out there, but the dodgy ones can be avoided by sticking to sellers with a high rating over a period time longer than a year. Also, if the price sounds too good to be true...
Coincidentally, just replaced my Samsung S6 with a OnePlus 3T that I bought on Lazada last week. Working great unlike the S6 that was freezing up on me with increasing frequency. Looked around locally for a case, but everyplace said "no hab". Placed an order on Lazada on Monday for a case, arrived on Tuesday. As Idefix pointed out in his post, I look for sellers in Thailand, so delivery times have always been fairly quick.