Comparison question with implicit 再 zài?
&quot;可以便宜吗？&quot; = &quot;Can it be cheap?&quot;
&quot;可以便宜一点儿吗？&quot; = &quot;Can it be cheaper?&quot;
&quot;可以(更)便宜一点儿吗？&quot; = &quot;Can it be cheaper (more)?&quot; -- compare to cheaper price
可以(再)便宜一点儿吗？ = Can it be cheaper (again) -- repeat 'the action be cheaper
It may be easier to understand with different phrasing:

&quot;可以便宜一点儿吗？&quot; = &quot;Can you lower the price?&quot;
&quot;可以(更)便宜一点儿吗？&quot; = &quot;Can you lower the price (more)?&quot;
&quot;可以(再)便宜一点儿吗？&quot; = &quot;Can you lower the price (again)?&quot;

You can repeat the same phrase as many time as you want until you get the lowest price you can get.