I've interviewed hundreds of 'salespeople'. Very few deliver to expected levels because, if you think about it, they interview for a living. They're great at it.
A sales person's failings are almost always blamed on product, company, location, manager or price. Interestingly, to date, I have never ever interviewed a salesperson who puts their reason for leaving as "sacked" on their CV.
That goes for all, not just salespeople...
Really, if you want to get to know the real person behind the CV (no doubt, full of untruths) some nice questions to ask are...
"What was the name of your last boss?" (let them answer) "I'm a fan of other people's opinions, so if I called her/him up now, how would he/she describe you?". Pick up the phone as you ask this question.
'Sexy?'
Stare at their CV for a while and with a poker face,
(Like Clint Eastwood?) just ask "when did you last tell a lie?"
'When I last faced the Spanish Inquisition'
Almost all salespeople will tell you that they work hard. Ask them to describe what 'hard work' looks like.
'Do you want a hard worker or a good seller?' The best salespeople I ever managed/worked alongside were the laziest most unpunctual people you could ever meet. Frustratingly anarchic, full of humour but needed or wanted to hit targets. Not always for the money either.
If they say they work well under pressure, ask them to describe a situation when they were really under pressure.
'Office Party...Mary from accounts' Whatever their answer, question it by asking why they let themselves get into that situation,
'if you'd seen mary from accounts' 
what they did to ensure it didn't happen again and what they applied since then to stop the problem reoccurring.
Married her...
I hope these help. My advice would be, every time, to get references, no matter how taken you are with the person. Speak to former employers and ask if they would employ them again. A 'no' tells you all you need to know in most instances.