How to flip Prayer regeneration potion(1) in OSRS

Flipping Prayer regeneration potion(1) on the Old School RuneScape Grand Exchange currently makes about 1,220 gp profit per item after the 2% GE tax: buy near 18,870 gp (the instant-sell price) and re-list near 20,500 gp (the instant-buy price).

• Buy at (instant-sell): 18,870 gp
• Sell at (instant-buy): 20,500 gp
• Margin after 2% tax: 1,220 gp (6.47% ROI)
• Buy limit per 4 hours: 2,000
• 24h volume: 4,128 (liquid)
• Max profit per limit cycle: 2,440,000 gp on 37,740,000 gp of capital

The flip, step by step

1. Place a buy offer at or just above 18,870 gp (the current instant-sell price).
2. Wait for the fill. Prayer regeneration potion(1) is liquid right now, so expect fills within the hour at reasonable prices.
3. Re-list at or just below 20,500 gp (the current instant-buy price).
4. The GE takes 410 gp tax (2%) per item when it sells, leaving 1,220 gp profit each.
5. Repeat up to the buy limit (2,000 per 4 hours), a full cycle is 2,440,000 gp on 37,740,000 gp of capital.

Margins move constantly. Re-check the live Prayer regeneration potion(1) numbers and price chart on GrandExchange.com right before committing.