Addresses are not handed out one at a time. A provider receives a subnet and distributes it among clients, and reputation sticks to the block as much as to the individual address.
What neighbours mean
Your address differs from the next one by a single digit and belongs to the same owner. If half the block spent months sending spam, the block goes onto lists as a whole — and you go with it, having done nothing.
This is where «I bought a new proxy and it was immediately bad» comes from. The address is new to you, not to the network.
What to look at
Two simple signals. First, who owns the block: the organisation name and the autonomous system number. A datacentre there means the address is not residential, whatever the listing calls it.
Second, whether the address appears on public blocklists. There are many services and any of them will do: what matters is the fact of a listing, not which list.
What to do about it
Before buying, ask for a trial. A seller who refuses is saving you time — it means there is nothing to check. After buying, demand a replacement while the refund window is open, not a month later.
The full check order is in testing a proxy, and the substitution tricks are in how sellers cheat.
What a clean subnet does not guarantee
That the account survives. The address is one signal among several: there is also the device fingerprint, the behaviour and the account's own history. A clean proxy removes one item from the list, not the list.
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