I use to do this successfully for many years. I could sell for a few cents less than Amazon. Due to buying gift cards at Kroger with a 5% Cashback card. In addition I would also get 1000 fuel points per $250 that I could sell for $20 easily. So each $1000 in sales would net minimum $130 margin. Accounting for selling fees of around 10%, I could clear around $30 per $1000 even at breakeven or below Amazon prices. I would also be able to sell many items for more than the Amazon cost.

It worked well for several years with millions in sales, all automated. It became untenable though as Cryptocurrency facilitated people buying Amazon gift cards with stolen credit cards and cashing them out at 30-50% of face value.

So the market became saturated with scammers selling considerably cheaper than Amazon. For a time maybe 6-4 years ago you could get pretty much anything from Amazon on eBay for around 20% less and shipped direct from Amazon via prime.

Amazon eventually shut it down though and if you meet some very strict gift card threshold they will just steal your balance. People still do it, but large scale automation isn't really worth it any longer.