If you’ve found a home you want to buy, the presence of Poly-B piping shouldn’t automatically disqualify it if everything else is in good order.
However, make sure you know how you’re going to address the plumbing issue before you make an offer on the house.
Hire a qualified plumber to inspect the home’s plumbing system. Get an estimate of how much it will cost to replace the plumbing system and deduct that cost from your offer. Or, have the seller agree to replace the system before the sale.
If you’re going to replace the system yourself after you’ve taken possession, make sure you’ll be able to find home insurance for the house in the meantime.