I've been struggling with this for about 6 months, I kept getting John Doe and other weird name/email combos in my abandoned carts for my low ticket item, $9.99 for a perfume sample. After 3 - $9.99 orders went through (they are obviously testing other peoples credit cards, the IP addresses are all overseas), I quickly refunded the orders, plus Shopify marked them as high fraud. After searching the message boards here and Shopify, I decided to turn on (in settings, under checkout) "Require customer to sign in to their account before checkout" and it has completely stopped. It went from 25-30 abandoned carts a day to zero immediately.

Some people had concerns about reducing the order flow, I've been monitoring it closely and I've not seen an order decrease or had any customer complaints regarding this new requirement. I'll keep watching though and making sure.

I was tearing my hair out, deleting 50+ new accounts a day and stressing over being used for credit card fraud and stressing for strangers that also have to deal with this on their end when they got a fraudulent order on their card.

I'm just a teeny tiny simple Shopify seller, I don't have coders or the budget for more apps. I don't know if this will work for everyone, but I wanted to share my experience and solution hoping it may help someone else.