I was waiting to post this for the
bounty program, but that takes too long so I'll post it already:
Your exchange can be gamed!
If I create an exchange now, the Letter of Guarantee shows:
The current date is Apr 07 2021. Your swap will expire on Apr 09 2021.
~
Your exchange rate is 1 XMR = 0.00508826 BTC.
Your exchange rate is 1 BTC = 196.530837654 XMR.
Monero
went up about 6% in the last day. With some testing in the past week, I got 2 signed Letters with about 7% difference in exchange rate, that were still valid at the same time.
So by collecting different Letters of Guarantee, someone can wait for Monero to go up or down against Bitcoin, and exchange to a coin that's worth more. Your 4% fee is a given, but not enough to prevent a few percent profit by sending it to another (instant) exchange.
This is the reason why exchange rates usually expire after at most 15 minutes. Your site offers up to 3 days, I don't think that's sustainable.
I'm still curious about this:
What do you do when you run out of either Bitcoin or Monero?