He said he was looking for serious offers. Normally, "serious offers" means people that REALLY intend to buy the car - not people just throwing offers out. But, the internet is no place to make offers. I would think he means for those interested to come check out the car (or have someone do that for you if you are not local), and then make an offer - that might include a deposit if accepted.
When I want to show someone I am serious about an offer, I normally have a check, money order, or cash for them as a deposit to let them know I am serious. I also agree (in writing) that the deposit is non-refundable.
Then again, there have been a few times I have just brought my offer price in cash. That's about as serious as it gets.
On the other hand, some people say "serious offers" meaning they want way more for the car than anyone's going to pay (ie, don't waste my time with a ridiculous offer). I hope that's not the case here. But who knows. I would think the seller would give a little more indication of what he/she means.
Lots of interest for the first X60D to hit the market. I'm Excited to see these new generation of S & X come at healthy discounts in the used and CPO market. I'd be willing to pay up to 67k for this example.