This is one of those situations where it's best just to ask the person instead of asking a bunch of anonymous strangers on the internet. Everyone is different. For example, I usually don't mind it that much when people try to finish a sentence for me when I have a block, even if their guess isn't right the first time. Sometimes it can be a relief. But a lot of stutterers are really against that. I have the kind of stutter where I get blocked on a word and end up just standing there mid-sentence with my mouth open stressing to get a word out and looking like an idiot. If you don't want to finish their word, the only thing we can ask for is PATIENCE. I find it better when the other person at least maintains eye contact, at least it shows that they're still paying attention to me instead of losing interest. One f the absolute worst experiences I had in recent memory was standing in line trying to order a b-b-b-burrito at a busy Chipotle. Words that start with hard consonants like "burrito" are often very difficult to say and it was taking a while for me to get it out. I lost the attention of the employee even though I was looking right at her and trying to speak, and she ended up going to the person behind me in line and took their order. It happens sometimes in busy bars too when I'm trying to order a m-m-miller lite. I try not to blame other people, but it still feels absolutely awful to be ignored like that. Hope this helps a little, but your best bet is just to ask them. A lot of non-stutterers think it's like a sensitive subject that shouldn't be brought up, but I really don't mind talking about it with others. I once had a total stranger ask me "do you have a stutter?" within like a minute of talking to him. Some people might think that's a rather bold (and possibly inappropriate) thing to ask, but I really didn't mind it at all. It actually took a lot of stress off since I usually do my best to hide the fact that I stutter.