I entered Nicaragua from Honduras in the middle of the night on King Quality bus. I got neither a entry stamp nor a Tourist card at the entry point and thought this might be a problem when I exited. However, t never caused any problem when I left to CR. The driver did handle the formalities for me.
BTW, the border crossing is quite easy with lots of vendors selling food and drink, and a couple of duty free shops.
I was also warned about the money changing coyotes but I actually got a better exchange rate from them than any of the banks I dealt with. Just do a rough calculation first so you know what to expect and count your money in front of them. The guy was actually very pleasant and we had a good laugh about my canadian bills which he liked but declined to exchange.
The Costa Rican side of the border is very modern, even with A/C while you line up.