What the customer sees
Their own bills with dates and amounts, the deliveries against them with vehicle and date, the payments they have made and how those were allocated, and the closing balance. Only their own account — never another party's, never your rates to anyone else, never your stock or your margins. They log in with their own credentials in a browser; nothing is installed.
Why it changes the relationship
A contractor who can check his account at eleven at night does not ring you at eleven in the morning. More importantly, when he does disagree, both of you are looking at the same screen rather than at two different records — which turns a dispute into a lookup. For regular builders and contractors this alone is often what justifies moving off a register.
You stay in control of what is shared
The portal is enabled per party, so you decide who gets a login. A walk-in customer does not need one; a builder taking material across three sites probably should have one. Access can be withdrawn at any time. Nothing about your purchase side, your other customers or your business figures is ever visible through it.
Alongside statements, not instead of them
The portal answers the question when the customer thinks to ask. The monthly statement puts the answer in front of them whether they asked or not, which is what actually moves money. Shops that do both — a portal for the regulars and a statement on the first of the month for everyone on credit — recover faster and argue less than shops that do either alone.
Who to give a login to
Not everybody needs one. A walk-in customer paying cash has nothing to check. The parties worth enabling are the regulars carrying a running balance — contractors, builders, dealers, anyone you send a monthly statement to. For those, the portal converts a stream of phone calls into something they answer themselves, and it makes the eventual disagreement a lookup rather than an argument. Introduce it when you send the first statement, so the two arrive together and the customer understands what they are being given.