Cannondale Aficionados / Owners

Don't think there's a rules in checking tyres clearance, if they're concern about it, they can simply ask their mechanic to check it for you while you observe.

Wow, if you went into a LBS they'd be overjoyed at the fact you bought TWO bikes from them, who are they to question your motives?! They also probably wouldn't give a shit if you whipped the wheels out and gave them a go in the frame, or even did it for you.
But, to be fair on the Evans guys, they have no autonomy over their jobs, they have rules, they have managers, it's a corporate system with so many levels nobody has the freedom to really use discretion and really help a customer.

Evans - but you're only allowed one

Verboten!

Me- Hi, I've ordered two CAAD12's, one 56 and one 58 for a test ride
Evans - you can only order one
Me - well, I ordered and paid for two, they're both in the workshop
Evans - but you're only allowed one
Me - are you saying I can only ride one?
Evans - I'm just saying it's against the rules, I guess you can ride them

Ordered a Cervelo R2 and S2 to try from Lesiure Lakes (a smaller chain) with the intention of only buying one, shop more than happy to do that for me.

Alright, spoken with Evans internal.

If you paid fully for all those bikes, then it shouldn't matter.

If you paid only the deposit, then only one at a time.