I've done a few times and no problem. I just told them I had no idea of the exact dates and thus will plan when I know. On one occasion, I did request the officer to stamp me for a 5+ month (the usual was 3 months) as I might be staying for that extended period. I flew back a day before the B2 expires.

By law US airlines are required to let you cancel your trip upto 24 hours after you book it for a full refund. See https://bkpk.me/easy-return-tickets-for-international-travel... for more info.

In the past I've used this to great advantage by booking the outward and return legs of the journey separately. You can then cancel the return leg ticket and book a replacement later.

At the airport present tickets of both the original outward and return legs; as long as you don't overstay a visa there shouldn't be a problem. Obligatory note that this should not be taken as legal advice.

a one way international ticket usually costs about 80-120% as an equivalent class round way ticket, due to different price buckets.

You have to be flexible somewhere - either on date or price.

Another option is traveling on a low-cost carrier who generally sell outbound and return segments separately.

Can't you change your return ticket once your there? As long as you don't overstay you should be fine.

Will it not cause you be banned indefinitely due to visa fraud?

Why so? There's no chargeback involved if you call the airline to change your return flight's date. At worse the airline will charge something extra for the trouble depending on the type of ticket you bought.

Very rarely, most of the times there is a hefty change fee unless you bought a refundable ticket.