Wetspot,
I would find someone knowledgeable about the level of ATM usage in your area. Don't go by someone or group of individuals obsessively biased against ATMs. Give out $5 bills like we do. Make sure the ATM is solidly inside a solid wall basically the same precautions as used with "an in wall bill
changer or bill to bill breaker".
Granted this may not be true for all areas but ... it is very unlikely that we lose our specific car wash customers because of our ATM format. Especially in our area ... since so many a no hassle no fee because of our local credit unions & banks competing against the big boys by offering free ATM use.
Like Earl pointed out a separate attached box for the bill acceptor is less of a risk than having it on the whole
coin box with all its accompanying more so electronic goodies inside. As far as spending more ... once the customer puts in a larger denomination cash item in the box ... I observe a similar effect as the "lulled feeling" from
credit card count up. Actually more so IMHO ... since the customer can stop precisely when done vs with a high denomination cash item. We actually have had some customers put a $20 bill &/or request that ability since the sign on
Etowah's box states 1s,5s, & 10s. That does not mean we don't have $20s programmed in ... since it is no problem with Dixmor 7 timers.