Is it possible to market-buy from the stellar distributed exchange? Or do you have to get the current sell offers and construct a bid for exactly the price of what people are willing to sell?
The Stellar Laboratory is an awesome tool/resource where you can answer questions like these for yourself and explore how Stellar works...
For instance, here is an orderbook for "NATHAN"
There is 1 offer currently available. Use this keypair to create a buy offer for those NATHAN
Public Key GAMZNHJS3QCM2FJXXU4V2S2CFRVRQYTSIQFIK2H3V72WB3S7IVE5ONZW Secret Key SB3T5DEZMCYNOFW4ENGKX26LEZVYKCK5LZ4ZUKHNSK346BAGPWGHXTII
The Asset was created by this public key and asset code is NATHAN.
When you offer up XLM, first set the XLM price to 9999 and then to 0.0000001 and you'll see what happens first-hand.