My gut feeling about feeding lizards to boas, particularly "feeder lizards" is that they would very likely carry diseases and parasites that could harm your Dumeril's Boa. I don't know your individual pet store, so I can't say that they definitely have bad lizards or anything. What I can say definitively is that unlike rodents, lizards are reptiles, and therefore much more similar to your boa - any disease that a rodent may harbor would probably not do anything to your boa, however, any disease that a lizard would carry probably could do some nasty things to your boa.
I would think that if you talked to the staff at the pet store, you could probably rub a mouse on a lizard without having to buy anything. If not, if you buy only one little lizard, you could keep it alive and use it to scent multiple rodents... though there are many lizards I would really love to keep but I think lizards in general are too needy for my tastes.
Another thing that does really matter, as I kind of mentioned before, is how the food is presented. A lot of people who keep snakes disagree with me on this, and I have a feeling that even more people in this forum will disagree here, but I use what I call "feeding bins" for all of my snakes. The biggest argument against this is that to use a feeding bin, you have to move (possibly stress) an animal that is not feeding (probably already stressed) to a new container to try to get it to relax enough to feed. This is true, and it can't work 100% of the time for EVERYONE... but it does work very well for me.
I use plastic totes that I buy cheap; tupperware/rubbermaid types with locking lids. For my little ones (currently my Dum fits this category) I have a 19qt bin that has a small floor space, and a proportionately tall heighth. I don't cut air holes because I don't leave the animals in the bins long enough to have to worry about air supply, but if you were to decide that you're not comfortable doing that, use a drill and drill from the inside to the outside, to reduce any burrs that a snake could hurt itself on.
What I have done in the past for more reluctant feeders is to place the food item in the bin first, so after I place the snake in the bin, I don't disturb it again. I do this when the prey item is either pre-killed/thawed, or alive but young enough that it cannot hurt the snake (rodents that don't have their eyes open yet). Obviously, when handling the snake, make the transition between the cage and the bin as short and stress-free as possible, (and though it sounds hypocritical) use slow movements, again so you don't stress the snake. Gently place the snake in the bin, and close and lock the lid. Then cover the bin with a blanket or beach towel, so that it is dark, and keep any loud and boisterous friends, spouses, kids, dogs, etc. out of the room if at all feasible. Set a timer for 30 minutes and leave the room yourself. After 30 minutes, tiptoe to the bin and slowly peek under a corner of the towel and see if there is any progress.
A lot of poor feeders are stressed out by a live prey item, and will huddle at the opposite end of the bin. This is where using a pre-killed prey item is best, and the small floor space of the bin comes in handy. Sometimes snakes that are not neccesarily bad feeders, but are easily stressed out by their captive situation (whatever the reason), will leave the area that you have left the prey in, especially when they are fed in a large enclosure. This is because YOU are bigger and higher on the food chain. Seen through the eyes of your stressed out captive, maybe you've left "bait," but whatever your motivation, you are big and you were just over there, so that is the last place your snake wants to be. If the enclosure is large enough, the snake will just completely avoid that area, and not realize that there is food over there. So goes my little theory anyhow. The smaller floor space of the feeding bin is key - this way it is harder for the snake to miss the fact that there is a prey item in the box with it. This goes along with the shoebox theory that has already been suggested in this thread.
Also, if you are presenting the prey with forceps or anything, a lot of people move too fast (scary!), or too directly toward the snake's head (more scary!). If you notice when you handle a snake (hopefully NOT the one that is being reluctant to feed), even snakes that are not head shy don't like any object to directly "confront" their face. You approach snakes' heads from slightly below or behind, so as not to be scary. Similarly, when presenting prey, anything presented straight-on will be received as a hostile confrontation; instead, I have found that presenting a prey item to just one side of a snake's head works better. Also, if your snake begins to show interest and then falters, slowly back the prey away. Oddly enough, this tends to spark more interest.
I know this got really long, and I apologize, but these are some general tips that I have used in the past with many different species of snakes. I hope this helps. 
~Rebecca
-----
1.1 Ball Pythons (1.0 '05 Ghost, 0.1 '03 Normal)
0.1 Dumeril's Boa '04
0.2 American Pit Bull Terriers (40 lb darling lap dogs)